Anger is a complex reaction. It's best to explore the trigger & develop useful reactions to it. Anger won't go away until the underlying cause is discovered. Four years of classes in psychology & communication were my therapy, so I didn't waste my time @ Cle State U. Do you mean physical "pain" or psychological?
get a pencil and paper and start writing what your angry about. why you are hurt and what can be done to prevent it from happening again.write until you feel you have it all down. then put the paper away for at least a few hours then go back and read. You will be amazed at the stuff you write down.
Find a nice quiet place (even a dark closet) and think your problems/solutions,or meditate. Visualize the universe and create a big blob to put the problem in. Think on all your problems, cause of pain or anger, and put them into the big blob, making it bigger and bigger. When you've put everything into it, throw it out into the universe....let the Creator handle it all. You'll be surprised how such a visual exercise can help you. Repeat if you get troubled again, but try to just leave it in Creator's hands.
This might not work for you but for me when I was your age and younger I would find some place where I could be completely alone and scream untill I couldnt any more, it could work if you scream into your pillow, pain well it depends on if its physical or mental pain.
I know this sounds kinda annoying, but RUN! I thought it was a stupid idea before, but the other day when i was walking with my friend we started talking about our principal who i cant stand and i got so mad! for some reason i just started running! By the time i stoppped i felt so much better!