From time to time a red spot develops on the glans of my penis. It is absolutely painles, not itchy, about 4-5 mm in diameter, roundish (maybe a bit more elliptical). Sometimes there are two at a time, but no more than that. They develop over the course of several days, maybe a week, after about a month the surface hardens and a layer of skin comes off, this, too, is painless. After yet another month (approx) it disappears on its own, with no treatment. I am 34 years old, have never had unprotected sex (or blood transfusion, or shared needles, or anything of the sort), and in fact it first appeared even before I was sexually active. It lasts about two months, disappears, then comes back on any part of the glans a couple of months to a year or two later. It is definitely not an STD (see reasons above), but very embarrassing. Any ideas what it could be, and how to treat it to go away faster?
(A dermatologist has seen it a few years back, but didn't pay too much attention to it, so that wasn't too much help.)
Thanks!