It sounds like we have similar symptoms. I had protected sex almost a year and a half ago (August 2008), and periodically I get red or pink bumps (more like spots, since they are not raised) appear on the head of my penis. These spots have been showing up, off and on, for maybe a year. I'm confused because I have only had unprotected sex once in my life back in March 2007. After that there were no signs that I had caught anything from her.
Friction from masturbation or clothing seems to cause most of the irritation. I found that Neosporin helps. If symptomatic, I will put it on at night, and in the morning the spots are usually gone.
I've been worried about herpes, but I can't find any pictures online that match the symptoms I have. They have never ruptured, scabbed over, or discharged anything. This gives me hope that it isn't herpes, but I know that symptoms can vary in type and severity.
might be fordyce spots which are very common.