In college I was high and drunk and not totally "up" for sex, but I hooked up with a girl and gave it my all anyway. Things were going this way and that. I should not have been attempting sex in my state. The next day, and for like a week, my penis was black. I probably should have gone to the doctor, but I was too chicken to,show up and say, "gee doc, I don't know what happened. I was too high and drunk to get a solid erection and I did some damage." In a week or so the bruising was gone and I was fine. If it doesn't get better, see a doctor.
Otherwise, ice it up!