When you are an enlightened Buddha do you have no more worries or fears and desires?

I think this would depend on what you mean by "worries and desires." There are certainly supernaturalist Buddhists who would argue that an arahant is literally, physically immune to such things.

But I'd argue against that; human emotions (at least to some extent) are the product of the brain and brain chemistry. Arguing that sitting and meditating can fundamentally alter brain chemistry to the extent that--for instance--you would feel no "desire" for water even if you hadn't had anything to drink for 3 days...well, it flies in the face of neuroscience. Likewise, doubting and worrying about your health are just things that brains do. It is unlikely that any spiritual realization would cause these normal processes to stop.

I think, in the modern world, a more reasonable interpretation is that an arahant feels cravings, fears and doubts as acutely as we do, but sees them clearly as unskillful products of greed, hatred, and delusion--and is therefore not bound by them and does not suffer because of them.

Zen has a bit to say on this subject:

'As far as Buddha-nature is concerned, there is no difference between an enlightened man and an ignorant one. What makes the difference is that one realizes it, while the other is kept in ignorance of it.'

(Hui-neng / Daikan 637 - 713)

And here is Sogyal Rinpoche:

'When you realize the nature of mind, layers of confusion peel away. You don't actually "become" a buddha, you simply cease, slowly, to be deluded. And being a buddha is not being some omnipotent spiritual superman, but becoming at last a true human being.' (The Tibetan Book of Living and Dying)

An enlightened Buddha or an arahant never experiences worries, fears, or cravings like ordinary humans even if they appear to. After enlightenment an individual can have wishes, wills, etc...but not in the same way that an ordinary person does.

In regards to health, The Buddha did heal himself on occasions, and could stay alive for an entire world-period:

"And the Blessed One said: "Whosoever, Ananda, has developed, practiced, employed, strengthened, maintained, scrutinized, and brought to perfection the four constituents of iddhi power could, if he so desired, remain throughout a world-period or until the end of it. The Tathagata, Ananda, has done so. Therefore the Tathagata could, if he so desired, remain throughout a world-period or until the end of it."

..... Then it occurred to the Blessed One: "It would not be fitting if I came to my final passing away without addressing those who attended on me, without taking leave of the community of bhikkhus. Then let me suppress this illness by strength of will, resolve to maintain the life process, and live on."

And the Blessed One suppressed the illness by strength of will, resolved to maintain the life process, and lived on. So it came about that the Blessed One's illness was allayed." - Maha-parinibbana Sutta

After enlightenment The Buddha was doubtless, fearless, and always in bliss regardless.

The Buddha and arahants described this bliss and happiness many times:

"Before, when I has a householder, maintaining the bliss of kingship, lord, I had guards posted within and without the royal apartments, within and without the city, within and without the countryside. But even though I was thus guarded, thus protected, I dwelled in fear — agitated, distrustful, & afraid. But now, on going alone to the wilderness, to the root of a tree, or to an empty dwelling, I dwell without fear, unagitated, confident, & unafraid — unconcerned, unruffled, my wants satisfied, with my mind like a wild deer. This is the compelling reason I have in mind that — when going to the wilderness, to the root of a tree, or to an empty dwelling — I repeatedly exclaim, 'What bliss! What bliss!'" - Ven. Bhaddiya, Kāḷigodha Sutta

"'Now, I — without moving my body, without uttering a word — can dwell sensitive to unalloyed pleasure for a day and a night... for two days & nights... for three... four... five... six... seven days & nights. So what do you think: That being the case, who dwells in greater pleasure: King Seniya Bimbisara of Magadha or me?'

"'That being the case, venerable Gotama dwells in greater pleasure than King Seniya Bimbisara of Magadha.'" - Cula-dukkhakkhandha Sutta

"Any sensual bliss in the world, any heavenly bliss, isn't worth one sixteenth-sixteenth of the bliss of the ending of craving." - Raja Sutta

And the Lord Buddha, perceiving that, on this occasion, pronounced this solemn utterance: "'Happy is the solitude of him who is full of joy, who has learnt the Truth, who sees (the Truth). Happy is freedom from malice in this world, (self-)restraint towards all beings that have life. Happy is freedom from lust in this world, getting beyond all desires; the putting away of that pride which comes from the thought "I am!" This truly is the highest happiness!'" (Mahavogga 1.3)

"cessation of perception and feeling" is described as the very most extreme form of pleasure:

"And what, Ananda, is another pleasure more extreme & refined than that? There is the case where a monk, with the complete transcending of the dimension of neither perception nor non-perception, enters & remains in the cessation of perception & feeling. This is another pleasure more extreme & refined than that.

Now it's possible, Ananda, that some wanderers of other persuasions might say, 'Gotama the contemplative speaks of the cessation of perception & feeling and yet describes it as pleasure. What is this? How can this be?' When they say that, they are to be told, 'It's not the case, friends, that the Blessed One describes only pleasant feeling as included under pleasure. Wherever pleasure is found, in whatever terms, the Blessed One describes it as pleasure.'" - Pañcakanga Sutta

Many imagine this type of "bliss" as something like relaxation, or a blissful state, but it isn't so, those are merely other "states". It really is the most extreme form of pleasure and happiness, unimaginable, indescribable.

I first experienced the "deep relaxation" state, very peaceful and tranquil, and thought that must be what enlightenment must be like, but then I experienced a higher more blissful state and thought that must be what enlightenment must be like, but then I experienced and even more enjoyable higher state....so eventually I concluded that these higher states and feelings are merely feelings and states, incomparable to the enjoyment that isn't a state or feeling.

The highest state I've personally experienced is extremely enjoyable, you feel full of confidence, fearless, doubtless, sorrowless, worry-free, care-free, stress-free, full of extreme joy. The other forms of happiness, fun, and pleasure I've experienced pale in comparison.

When entered that state I saw how the other states I experienced were merely temporary transient feelings, it's difficult to explain.

Having seen my own errors I know that I haven't achieved perfection or enlightenment yet but maybe eventually I will.

When describing destinations, The Buddha uses a clever analogy to explain what enlightenment is like:

"By encompassing mind with mind I understand a certain person thus: 'This person so behaves, so conducts himself, has taken such a path that by realizing it for himself with direct knowledge, he here and now will enter upon and abide in the deliverance of mind and deliverance by wisdom that are taintless with the destruction of the taints.'

And then later on I see that by realizing it for himself with direct knowledge, he here and now enters upon and abides in the deliverance of mind and deliverance by wisdom that are taintless with the destruction of the taints, and is experiencing extremely pleasant feelings.

Suppose there were a pond with clean, agreeable, cool water, transparent, with smooth banks, delightful, and nearby a dense wood; and then a man scorched and exhausted by hot weather, weary, parched and thirsty, came by a path going in one way only and directed towards that same pond. Then a man with good sight on seeing him would say: 'This person so behaves... that he will come to this same pond'; and then later on he sees that he has plunged into the pond, bathed, drunk and relieved all his distress, fatigue and fever and has come out again and is sitting or lying in the wood experiencing extremely pleasant feelings.

So too, by encompassing mind with mind... extremely pleasant feelings." - Maha-sihanada Sutta

I think it's a great analogy. It reminds me of a time when I was riding my bike one day and after I became very tired and exhausted I decided to stop by a river. The river looked clean and transparent so I jumped in and swam in the river, it was very relaxing and pleasing.

The term buddha is also used in Theravada to refer to all who attain Nirvana.

please let me make a correction, in Theravada a term used to all who attain nibbana is arahant

Buddha is one who only attained nibbana on their own having discovered the path to nibbana for themself without reliance on anyone else

But does this all mean that fe Siddartha Gautama never worried about his health

i think it means that as a Buddha he didn't

or was never doubting about hisself whether he was doing good or not?

as a Buddha he could do nothing BUT good, because with awakened beings virtue and skill are natural, it's like a compass hand which points at only one directon

Doubt is one of 10 fetters, which is abandoned at as early as the sotapanna stage not to speak of the arahantship