What Does Burning Sensation During Urination Indicate?

I have seen 3 different doctors including the ER doctor. All tests have come back negative. (No Chlamydia/Gonnorhea, no yeast, no bacteria in the urine). I received Azithromycin about 3 days ago and took what was prescribed. Although I've noticed a little significant change, I've developed a fever and it still feels like razors and fire when I urinate. My whole body hurts and I'm just at a loss for answers now.