What Causes Discoloration Of Penis?

My penis glan has had a reddish, sometimes purple, discoloration for over a month now. The head of the penis itself isn t always painful but it hurts to have things (shorts) brush up against it. Within the first week there was some sluffing of the skin near a painless ulcer. Dr. thought it was herpes. I was checked and my tests came back negative (for all STD s). I had an alergic reaction to a sulfa medication shortly after my penis changed color. I ve since stopped the medication but my penis hurts just the same. Dr. s said it was probably balanitis but couldn t give a cause. Checked for fungal and came back negative but put me on antibiotics (doxycycline) in case of infection. Nothing has changed. Now it still hurts, my scrotum feels uncomfortable and I have to urinate a lot. I saw a urologist and he checked my prostate, which he felt was large for a 30 yr old and figured it was probably prostatitus. And tonight I noticed a rough patch of small bumps just below the penis glan. I m a mess and don t know what to do because no one can say what they think it is.