I am a 40 y.o. caucasion male, 6'3"/225 lbs. From September to the Begining of November of this year (2004), I had 3 incidences of unprotected vaginal intercourse with a female, who, after the fact told me that she had many partners.
On 17 December, (so about 6 weeks from the last incidence) a "bruise" appeared about halfway up the shaft of my penis. It is black/blue/purplish, roughly circular, not raised, about the size of a quarter. In the center is a small red area just smaller than a pecil eraser. It is not painful, does not itch. I dont not recall any injury that would cause a bruise either (e.g. no hard masterbation, or other force that would cause bruising).
I have never had anything like this before, and I have no other health issues, except some hypertension (High BP). Could this be an STD? If so, which one(s) would you suspect? Should I get it checked out? If it is, I don't want to pass it on to anyone.