What Causes Vomiting, Abdominal Pain, Black Diarrhea, Bloating And Dizziness?

I am 34 yrs old, female, and have been having bouts of intense vomiting,(yellow nasty tasting stuff) abdominal pain, black watery stools and bloating, dizziness.....my first instance was years ago, and the doctors told me to stay away from msg....Over the past four years I have had these bouts 5 times, about 6 months apart. I start throwing up violently and can't stop for days. End up in the hospital with and IV but they can't seem to find the problem. I have had this gastro picture taker tube down my esophegas 3 times, no ulcer...what could it be???? My last bout was this past thursday, I stopped throwing up Saturday but still have black watery poo. HELP