stomach problems

ok im sorry in head of time this is going to be kind of long. ok so I’ve been having stomach problems for the longest time. it started when I was about 6 and im 13 now. diarrhea, naushia, no vomitting though, thank goodness! well about 2 years ago I took a catscan and when I was about 8 I took an upper gi series. they found nothing. then in september of 2007 I had a colonoscopy and endoscopy and they said everything was fine. my doctor said its irritable bowel syndrome, stress, and and he said to change my diet and I did and im still having stomach problems today. it feels like a stomach virus a lot of the time. it hurts if I eat, it hurts if I dont. I’ve been taking a lot of days off of school because of it and I cant afford to miss school or anything else important. my dad doesnt like me staying out of school at all and I dont blame him but I cant help it its out of my control. does anyone have an idea of whats wrong with me beside irritable bowel syndrome if there is? and if its just that how can I relieve the stomach pain and diarrhea? oh and by the way I know this is disgusting but I fart a lot. im really gassy haha. ok well anyway any advice on what to do?