Fencer

Hi all, I may just be paranoid here, and I'm actually a little reluctant to ask this question in this particular forum because some people see STD's if you have a hang nail (IE: seeing monsters in every shadow), but what the heck.
It's been about a year since I had sex (if not for the 4 times a day masturbation marathons I probably would have exploded). So I finally get back to my home city (was away working for a year), and call one of my old friends with benefits. She comes over and we have a good time.
Long story short, two days later the very tip of my penis hurts. Every time I flex the muscle, or squeeze the tip.
I've pretty much confirmed that it's not unusual that the penis is sore after extended intercourse (we went about 2 hours of just intercourse over a three and a half hour period at one point).
But it doesn't feel sore like a arm muscle when you lift for an hour. It is kinda a sharp pain when I flex the muscle.
Any suggestions?
It developed about a day after we had intercourse.
Any insight would be appreciated.
Thanks!