Im tired to show my penis and get no real answer

[myproblema]

The skin of the head of my penis in now dark almost completely, this problem began one year ago. I was sexually active back then, only with my girlfriend. Anyway, for no reason that I can tell the skin of the head of my penis began turning dark, when it used to be purple/ pink, also the skin is harsh (like sandpaper), only for a tiny spot that remains normal, in color and texture.
I’m a general doctor so let me say for sure that I haven’t any STD on me, been tested, because of this problem, always negative results. One Dermatologist told me that I got a lesion that hasn’t heal yet, he prescribed some ointments (cellular regenerator) that were supposed to help the healing process, one month an no change,  I went to another dermatologist an she said it looked like vitiligo, so I should worried she said!. And urologist told me that it looks like urine spots, be that he wasn’t sure, but he tell me no to worried.  
Having time past I tried:
• Primecrolimus for almost two months no change (color seemed to improve but I think it was because of the color of the cream that was white and maked skin look better)
• Tetrasil for one month no significant change (skin seems to be softer but color is the same)

I`m worried because I don’t know any person with the same problem, when the penis is not erected the PROBLEM look awful. When erected it can hardly be seen. I don’t see the problem getting worst but neither improving, please someone help me… I have even thought of microdermabrasion…