What Causes A Spot On The Penis?

Hi, I have a spot on my penis.. it apeared after having unprotected sex with my girlfriend. I had a UTI, yeast infection and this spot appeared too. I went to the doctor and tested negative for ghonoria, clamidia and HIV. The doctor said it was not a symptom of herpes and was probably caused by the yeast infection and uti.. several weeks later the spot is still there.