Correct meditation Technique I am subject to thoughts containing anger, hatred, resentment etc. which causes me lower back pain.
I am using medicines but useless because the relief is temporary.
I am a meditator but I watch breath at nose tip, which causes me more
tension after the session is over by 2 -3 hours.
I have read somewhere that watching breath at belly i.e. Dantian is also 
recommended.
I have tried it once and found it more relaxing.
What should I do? Watch breath at nose tip or belly button?
I have been doing nose tip meditation for six months which took me sometimes to thoughtless awareness - but did not solve my problems of physical pain and irritability
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 &amp; 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.