I have upper back and neck problems and my shoulders are out of whack also, unfortunately none of this has anything to do with big boobs!
I tend to sit twisted up in my chair and its a habit I just cant break so all I can say is thank god for my chiropractor. Every 2 weeks and it cuts down on the back aches and migraines I have gotten since I was 8. Just make sure you find a doctor that works with you. I get heat therapy, massage, stretching and then adjustment. Its great and feels as good as going to a spa!