Suggest Remedy For Red Purple Cyst On The Base Of Penis

Im a 22 year old, 6"2, 190lbs who has had unprotected oral sex in the last few weeks. Over the last 2 weeks I've develloped a red/purple "cyst" on the base of my penis. It's not too tender, but I originally tried popping it thinking it was a pimple. It's since gotten larger, and is starting to appear glossy on its surface. It was originally fairly large, but has gotten a bit smaller over the last week. Should I be concerned? What is this?