I am having diarrhea every 15 minutes, what can I do?

I woke up this morning with really bad stomach pains, and I used the toilet, but every 15 minutes since then, it has been constant, but the more I go, the less there is, and now its almost nothing. I tried eating cereal thinking it would help having something in my body, and literally when i finished, it went right through me. I tried Pepto-Bismal but that hasn't worked. What could this be?? help :(