HELP. I am very sick and nobody believes me. I think I am dying...?

I think I am dying. I have diarreah 24/7, I constantly feel like I'm going to throw up (and sometimes I do), I am ALWAYS tired, weak, and dizzy. I usually have some sort of infection, too (tonsillitis, UTI, bronchitis, kidney infections, you name it). This is a daily thing for me. On top of this, every once in awhile, I have some sort of horrible "attack" where I am absolutely doubled over with stomach pain. I start sweating, shaking, throwing up, my heart races, I p out, etc., and usually somebody I know rushes me to the E.R. ...only to have them tell me they do not know what is wrong, or worse, that it is a panic attack, or that I fainted from standing up too long (I also have very low blood pressure) or not eating or drinking enough. It is not a panic attack. It is a PHYSICAL problem. I have been tested for intestinal diseases (Chrons, etc.) and all tests are negative. Xrays, scans are fine too. I am a 31 y/o white Irish male and I eat right and exercise when I'm not too sick!!!