on penis noticed two black/puprlish dots, painful when erect.

so im 15, had sex with two girls, first unsafe (back when i was about 13) and seconldy was safe, except for when she gave me head for like 10 seconds and freaked out because she had an ulcer or something that leads to herpes or something like that. Anyways, I seem to have noticed yesterday that I have one or two (maybe even joined together) dots under my forskin, which only hurts when my penis erect. It's not like a throbbing pain, but more like it's stinging like some one has cut my penis just a little bit, but it was irritating and i couldn't ejaculate, it started to sting more from touching it whilst erect so i gave up, ran it under some water to cool it down or what ever.