If you don't think it could be from sex sounds like a yeast infection (thrush) - pretty common. Comes from time spent in a warm/humid climate. Can keep reoccurring - treatable with cream (canes tan) - apply lots daily for a bit and should go away.
If you think it could have been from sex then it may be genital herpes.
It is critical that uncircumcized males keep this area clean. Push back the foreskin when showering and make sure that you are not accumulating anything there. If this does not help, by all means check with your doctor, as it could be yeast or another infection that needs attention.
Do you eat Yogurt? if not, you might give it a try. When women get yeast infections we eat yogurt it helps clear it up. its the live yogurt cultures that it contains. this happens alot when we take antibiotics or after menstral cycle.