You're sick. Give yourself a break. Rest, take meds if you need to and go to see a doctor. You shouldnt even meditate if you don't feel like it. Its not a competition. Be gentle to yourself. Would you withhold medicine from a sick child? If not then you don't withhold it from yourself. There's nothing wise or spiritual about such thoughts or actions.

Consult a doctor regarding your sickness as soon as possible. As for Buddhism and sickness, you can follow a suitable meditation for that. This however had nothing to do with medicine.

I haven't seen any references in Buddhism saying not to have medicine.

If you have fever please consult a doctor and take medicine. I do not take a pain killer when I have pain. But I keep pain as my meditation object. I have taken painkillers less than twice in last three years. My experience without painkillers is shared in the following link.

https://dhammawheel.com/viewtopic.php?f=22&t=16532&hilit=

Only one part in five (taking to account there 5 Niyama) is due to Karma / Sankhara. Even if its, there is nothing preventing medicine from working, i.e., sickness was brought upon by a previous karmic reaction and the medicine also reacts and cures. This is Kamma niyama and Dhamma niyama fully or partially cancelling out the net result.

Also our bodies are prone to sickness for other reasons like say genetic reasons. So not every ailment is not Sankhara.

Sickness, what ever source, can be remedied by Payoga Sampatti¹, i.e., having sound knowledge, good reasoning and having good tactics, plans and methods to overcome the predicament. The final result may very well be decided by this than the source which triggered it.

As any sickness, when you get it, it is unsatisfactory. Just observe the sensations this brings, while taking medicines and treatment!

Also make it a point to educate your friend in this also!

¹

Condition 4 - Payoga Sampatti And Payoga Vipatti

Payoga Sampatti

Payoga sampatti means the combined effect of sati (mindfulness) viriya (vigilance) and nana (knowledge). Here knowledge means harmless knowledge as well as vitakka (good reasoning). Vigilance, effort, alertness, insight, wisdom, intelligence and mindfulness - all amount to payoga sampatti. In the realm of Devas and Brahmas, payoga sampatti is not so prominent. But in this human world it is of paramount importance.

Human beings have no akusala kamma so powerful as to bring immediate effect. The power of past deeds depend on whether there is payoga sampatti or not to produce results and on the degree of payoga sampatti.

In a nutshell, people should not rely only on past kusala kamma for their well-being. They must also rely on the efforts exerted in this life. This payoga sampatti channels past kusala kamma to flow in the right direction. Of course some wholesome deeds done in the past produce good results at present, such as winning lottery or unearthing a pot of gold. But such events are very rare. In trade and commerce the effect of the past kusala kamma accounts for only one fourth of the prosperity achieved; the remaining three-fourth is due to payoga sampatti in this life.

Payoga Sampatti Can Stop Akusala Kamma

Akusala kamma can be divided into two grades: (a) Powerful or major kamma, (b) Feeble or minor kamma. Payoga sampatti cannot stop the bad effects of akusala kamma of the first grade. It can only soften the blow to some extent. For example King Ajatashatru killed his father. For this serious crime of patricide he was bound to suffer in Avici Hell. His payoga sampatti, however vigorous, cannot save his fate. Yet, due to his repentance and devotion to the Buddha, he was penalized in Udassa Niraya (a lesser hell) and suffered less than his due. This even Garu akusala (the greatest evil) can be mitigated by sufficient payoga sampatti.

Therefore if your evil deeds are not so bad as Ajasattu, you can lessen or stop the coming bad results. If you have done evil deeds such as abusing your teachers, showing disrespect to parents and elders, slandering virtuous persons, you can stop the coming evil consequences by mindfulness and sincere repentance.

You can nullify the evil consequences by prostrating in apology before them or, if they are dead, by doing the same at their graves. If you repentance and apologies are sincere, your payoga sampatti will ward off the impending evil results.

Similarly, feeble or minor bad kamma can be abrogated by greater good kamma here and now. Monks who have transgressed Vinaya rules of the lesser kind can rectify their misdeeds by following repentance procedures outlined by the Buddha. Thus even the effects of some moderately evil kamma can be stopped by the payoga sampatti.

Payoga Sampatti Brings Prosperity

People who have no faith in the Ti Ratana (Three Jewels) also have accumulated merits because they surely had done good in their past existences. This know-how, their perseverance and their diligence are praiseworthy. In addition to the welfare of the individual, they exert great effort to defend their country through science and high technology. (although some Buddhists severely criticize their endeavors as being akusala), no one can deny that these efforts bring about economic prosperity social development.

Such aliens who come to our country to seeks wealth and prosperity are found to be very vigilant, hard-working, skilful, intelligent and clever. Their know-how is far superior to ours. With foresight they select appropriate sites and places (pati rupa desa) for their enterprises because they have wide knowledge and experience. With so much payoga sampatti, their past kusala kamma has very good opportunity to produce effects and accordingly they become rich in leaps and bounds. If we, Buddhist citizens of Myanmar, should follow the path of diligence (sampatti) effort, we would also achieve prosperity and progress as they do. We all should seek knowledge and experience together with payoga sampatti for our national development.

Health Through Payoga Sampatti

Human beings born to this world are accompanied by kusala kamma which brings good health as well as by akusala kamma which brings ill-health. Conforming to health disciplines, personal hygiene, regular exercise and sufficient rest and sleep, adequate medical care, all amounts to payoga sampatti which leads to good health. For those with such payoga sampatti, their past kusala kamma will also take effect and enhance their physical well-being.

Hence payoga sampatti is the prime factor for kusala kamma to bear good fruits. Due to payoga sampatti one can gain knowledge, marry a worthy partner, get good friends and teachers and acquire wealth and status. It can also assist in the fulfilling of perfections which pave the way to Nibbána. In the constituents of payoga sampatti, knowledge is the first requirement. Second comes mindfulness and third vigilance, in whatever we do.

Payoga Vipatti

Torpor, laziness, lack of knowledge, forgetfulness, envy jealousy, anger, hatred and vain pride are all payoga vipatti. They stand in the way of success and prosperity; payoga vipatti opens the door for very powerful akusala kamma to take effect immediately.

Such powerful evils are present only in the mind-continuum of only a very few people. But smaller evils are always present in everyone, waiting to produce effects with the occurrence of payoga vipatti.

For example, children of good families lead good lives by seeking education, right livelihood, observing the Five Precepts; these wholesome acts, will prevent the evil results of the past to produce effects. If children are lazy, undisciplined, follow wrong livelihood, and breach Five Precepts; they are developing payoga vipatti. This in turn invites the past akusala kamma to take immediate effect.

To sum up, apart from very powerful kusala and akusala kamma, other ordinary kamma whatsoever may or may not produce results, good or bad depending on payoga sampatti or payoga vipatti. For people with payoga sampatti, only kusala kamma will prevail and akusala kamma will have no chance to produce effects. On the other hand, for those with payoga vipatti, good kamma results have no place; only the evil akusala kamma will take result. People whose lives are ruined by their akusala kamma due to the prevalence of payoga vipatti are not uncommon. They can be found in almost every community.

Source: Abhidhamma In Daily Life by Ashin Janakabhivamsa

I just want this feeling of weakness to be over

I would focus my awareness of desires like "wanting feelings to be over", when they happen as they happen, moment by moment. You could be aware of the weakness as it occurs in your experience too.

But yes one more thing i realized today, the importance of healthy body

It's nowhere near as important as having a healthy mind. The only reason to have a healthy body is so one can have more time to cultivate the mind(at least this is the ideal aim in Buddhism)

Should I not take medicine in fever and just observe what is happening inside.

If the medicine is only to stop the pain then you should not take it, if you can. If you can't that's ok too but if you can't accept it then remember to accept that you can't accept it.

If it is a medicine that is an actual remedy for the disease instead of aversion to the truth of suffering then the medicine is more appropriate to take but you don't have to. We can learn a lot while we are sick but mindful.