constant UTI, flank pain, nothing is coming up on tests

I'm getting really frustrated with this issue. I have been to my regular doctor multiple times already and they've done a x-ray, and an ultrasound and nothing is coming up, it all comes back normal. When i went in for a uti, the doctor told me there was microscopic blood in my urine and that she would leave it for a urine culture and nothing came back on that either. I have been having flank pain on and off again since Christmas of 08 and it's getting frustrating with them not being able to tell me what's wrong with me. The pain is getting worse it seems, like now i'ts almost 4am and i'm still awake, i can't sleep anymore from the pain. The doctors won't give me anything for the pain either, the only thing they tell me is that they don't know what's wrong with me. If anyone has gone through the same issue or close please reply. I'm 19 years old, a tad overweight but that's easily fixable, and haven't had any other health issues besides polycystic ovarian syndrome.