Mackdaddy 11,
try to get your doc to refer you to a specialist, gastroenterologist if possible. They can diagnos many type of gut problems. You may just have irritable bowel syndrom, (ibs), ibd, (another bowel disease), crohns disease or colitis, illeitis, etc. But a gut specialist can probably help you.
Be strong and seek help now while you are young, be insistent, because to go through endless years of being treated for stuff that may not have anything to do with what you may have can be very unhealthy and debilitating.
I wish you the best of luck in your search.
Sharonh