What Causes Headaches, Lightheadedness And Vomiting?

Hello, just a few months ago I ve experienced a strange strain of symptoms and all the test that were given to me came up negative. The symptoms that I ve had included light headedness, diarrhea, vommiting, back pain (central and* lower) stomach pain (lower abdominal [pelvic]) shorness of breath, and headache. I ve been given a pregnancy test, UTI test, and STD tests and all have came up negative. I ve even had an ultrasound to rule out cysts and that came up negative. I have no idea of what would be the matter! :(