What Causes Reddish Blotch On Penis Head?

Hi. I am a 45 yr old male, married for 23 years. I have never had any sexual relations outside of my marriage. A couple/few months ago, I developed some symptoms with regard to my penis: I noticed one purplish/reddish blotch in one spot on the head. Secondly, I would feel a discomforting pain when I had an erection. There is no discomfort or unusual occurrences when the penis is not erect. Oh yes... a second blemish did develop on quite nearly the opposite side. I have already seen a urologist.. but frankly.. he didn t really inspire confidence in me: he seems genuinely puzzled and confused by the symptoms. He did start me on antibiotics, which did nothing for neither symptom. I had experienced genital wart-like symptoms waaayyy back when I was about 19years old.. but no manifestations of any kind until just recently... however.. these are not even a wart.. just a discoloration or blotch. I would appreciate if you could provide me with some insight and some possible causes to discuss with my doctor. This is unnerving, as I literally have only one sexual partner in over 23 years and it is interfering with intimacy, due to the pain during erections. Thanks in advance.