I completely feel you, i'm 18 have the same problem I just turned 18 years old and i'm lucky I didn't have this problem during high school or I swear I would have jumped from a bridge or something its seriously humiliating. I have to hide out from all my friends now it sucks.
I've had my proffessors laugh at me, I've dropped most of my classes where I sat close to people and I'm not taking courses until I get this sorted out. One thing is though, I have symptoms of this because I have problems with my bowel movements. I'm not sure if you have any but it would be a big help if you could post them here even though that feels like TMI kind of gross and what not, but when it comes down to it nothing is more important than figuring this out.
What I honestly believe I have, and what you most likely have is whats called an internal intussusception, I say that because when I read this thread: //www.curezone.org/forums/fm.asp?i=1785332#i
. I have his symptoms exactly and I suspect you might also.