I've havent been able to keep any food down for days, all I get is a stomach ache and bad diarheaa, what now?

This has happened quite a bit in my life. I'll eat something that my stomach doesn't agree with. Then I'm in the bathroom for a couple of hours. But then I can't hold anything down for over a week. Anything that isn't essentially bread and water goes right through me. The annoying part is that I still get hungry! But even still, its the same result. Ive tried Prilosec, Zantac, Pepto, everything. Whats wrong with me?