I had sex with this girl I didn't know and I used a condom. I now have this spot on the lower shaft of my penis, it's not a bump and it's just a spot of red. I think it may just be an irritation from the friction, and I just want to be sure. It doesn't hurt, itch, or anything. I had protected sex, so I'm not sure if this is something serious. Will this go away? Could it be an STD?