I also had a bad IBS experience in high school. It started out as panic attacks and developed into RLQ pain, costipation and difficulty swallowing food. I basically didn't eat anything solid for six weeks because I was afraid I'd swallow the food and it would get trapped in my throat and I'd die. I know, it sounds a bit insane. My father took me to the ER on two seperate occassions for gas pain that had be doubled over.
My issue was pretty much anxiety based due to some family issues, my boyfriend moving away to college and my anxiety about selecting a college for myself. I'm not sure what is going on in your life currently, but it might be a good idea to think about the stresses in your life. Are you getting ready to graduate high school and move on to the next thing? Are there alot of pressures in your life?
As well, my IBS issues pretty much went away except for the occassional flare up for the next 11 years. They came back recently, a month after I got married, moved and switched jobs. Everyone's triggers are different. Some are food and some are emotional. It's best to investigate all possible causes.
IBS comes on for alot of people during their teenage years. For me it started in the last year at school, which was bearable. But during college i kept having to dive off to the loo all the time because it got worse! I'm not sure what to say really, but don't feel you're alone, all the peeps on this board are very supportive and know exactly what you're going through