Correct meditation Technique

If you are having pent-up anger, hatred and resentment, then the maithri bhavana (loving kindness meditation) is what you should practice morning noon and night. It is not easy for everyone to properly do Anapanasati , and it is wrong advice to watch breath at belly. So if you have difficulty in watching the breath, first practice Asubha Bhavana and Dhathu/indriya Bhavana. You should not mix one meditation with another. You should get out of one type of meditation to get into another. Anytime when there is wandering thought, the concentration is not there. The appearing of a nimitta is a sign of concentration. When you develop an anapanasati nimitta, and practice it further, then you need a good knowledge of teachings (suttas) for you to overcome obstacles that you face.

If you are having trouble with anger, hatred, resentment etc. then there is a couple of methods I could suggest. Sakyamuni Buddha taught the four brahmavihara (love, sympathy, joy, equanimity) for countering the type of thoughts you are having. This is good for whatever type of Buddhism you follow.

Personally, I am a Pureland Buddhist and we chant the nembutsu in faith of Amitabha Buddha. By faith I mean trusting in the Buddha's power, and don't worry about things outside of yourself. I have found that this inward reflection on Buddha's power makes me more loving and compassionate to others.

Certainly a variation of meditative techniques may be effective, but modern science has shown that massage therapy effectively reduces aggression (see http://www.ncbi.nlm.nih.gov/pubmed/12458696).

I've found that monitoring bodily feelings helps you trace the root of the negative thoughts. So try monitoring your negative bodily feelings then massaging that area, it seems to work well temporarily (not but permanently).

I've attempted to trace where my negative bodily feelings come from (which causes me have negative thoughts, say negative things, and take negative actions) and I've traced it to early negative childhood experiences (from around age 5 or earlier). It seems that these early negative memories stay inside of us unconsciously, unknowingly until death unless we do something about it.

In order to permanently end the pains you have to deal with the negative memories associated with those bodily feelings which is more complicated.

Wise-reflection (yoniso-manasikara) is generally recommended as a preliminary practice to formal (anapanasati) meditation.

Here, the practitioner reflects/thinks thoroughly with reason & wisdom on the harm & dangers of anger, hatred, etc, in a manner conducive to give them up.

The Dvedhāvitakka Sutta describes the Buddha-To-be doing this practice before his enlightenment.

I'd suggest to leave anapanasati behind, do low-concentration ("dry") vipassana which will make you face and learn to face the anger (you will learn how to not attach to it, let it come & go, not judge yourself for it, not analyze and not make theories about the pain it causes), dtto for the back pain. There is nothing wrong with anger, it is your teacher just like pain; the attachment and unskillful dealing is the problem; by observing the pain or anger, you will get insight into yourself, and will learn to accept anger and pain as a part of you being human, and integrate it into your life skillfully, without (progressively) harming yourself and others.

(Explanation:) The reason for this is that people tend to use concentration (including anapanasati or brahmaviharas) to run away from conditions, instead of dealing with them. Those practices can be beneficial, but they have also their blind spots, and the best is to have a long-term teacher who can guide you here. Otherwise it likely that the ego will use metta-practice to re-affirm itself, such as persuading you about being loving and caring when you're perhaps full of anger and hate. I've seen on a few occasions people developing metta-crust on the top of stuff they never dealt with; which means (a) they learn to live with lie (delusion) instead of being in the present and in the truth (b) in more difficult situations, the crust breaks and I was very surprised how quickly the seemingly loving person turned into almost a hate monster; they regretted that themselves later, but did not understand what happened.