Have you had your appendix out? If not, have you mentioned the possibility of appendicitis? I've heard many stories about how it's improperly diagnosed until it finally ruptures, and you don't want that.
If you have, you're like me! And it sucks, believe me. The best thing you can do is try different doctors until you find one that actually cares, and when you do manage to find one, try to get them to run tests and help you, because they will, they have to, you just have to push for it because hospitals in general don't want to spend money.
Mention the possibility of adhesions as well, they're bands of scar tissue that form and can tug and twist your colon.
Hope you get some kind of breakthrough, chronic abdominal pain is no fun at all.