Vomiting and Nausea

I don’t know what's up with me, dry heaving until it hurts, and nothing ever comes back up. If I slam a huge glass of water or Gatorade it gets worse, drive heaving than becomes more frequent. However as I'm hydrated I feel better until I don't again. I'm on antibiotics for a urinary infection and it has almost all gone, yet I haven't been able to eat anything such as a solid food. I'm not hungry and am losing weight, and it's getting worse as nausea and drive heaves hurt badly. I take promethazine and Zofran.

I don’t eat, except half a cup of yogurt about every other day. Then I get diarrhea eruptive. After eating the yogurt my stomach in in pain for about 4 hours and my left side has sharp pains. This has been going on for about three weeks and I really feel sick and very tired but I can’t sleep.