I had bad acne when I was 10 and I had it up until I was 15. I went on accutane, and even though its not for everyone it helps. I've tried many medications and I went through the same thing too. I always had to wear shirts that came up to my neck! It was so embarassing. To ease the pain though, I suggest a soft lotion or cream. Any kind really, one that will make your skin soft. When I had more lotion on, the less it hurt. ( I think it hurts more when your skin is dry).
Try the lotion. Also, if you find that your back and chest hurts when you get out of the shower, it may be more sensitive since the hot water opens your pores. When you are just about to leave the shower, turn the temperature down so that it's luke-warm/cold and that may help also.