What is wrong with me? PLEASE help!

I am 18 years old and two years ago when I was 16 I had the worst abdominal pain...the only way I can describe it is it felt like contractions of some sort either right where my bellybutton is or a little higher. They started out not so bad but then they got really fast really quick to the point where they were literally debilitating. I would get down on my knees and I wouldn't breathe and I would cry and it was just awful. Late that night I went to ER and they thought it was maybe appendicitis so they gave me a CT Scan....nothing came up.
Then everything was fine for about a year or so and two weeks ago they showed up again. Only this time accompanied by vomiting and lots of diarrhea. Again, went to the hospital and they said I was dehydrated from the vomit and diarrhea and they thought I had gull stones so they gave me an ultrasound of every organ (I think) in my abdominal section accept my appendix because I told them about my previous experience in which the CT Scan came out clean.
Now, today, I am having them again. I am not vomiting (thank god) at least not yet, I am kind of afraid to eat. But I do have a lot of diarrhea so I am trying to keep hydrated. The "conctractions" aren't that bad right now but I fear they soon will be and I hate having to keep to going to ER- its timely and expensive and I am a new college student on financial aid on Medical - i don't have the money.

Please help me. I don't know what to do.