What Causes Red Blotches Below Foreskin After Having Unprotected Sex?

hello, could you please give me more information on my problem. i had unprotected sex and straight after i realsied a few red small blotches just below my head and foreskin. after a few days they seemed to go but now nearly three weeks later, my forskin looks a irritated red and have the blothes back along a couple of tiny spots. it could be fine one day then the next for the whole day its really itchy. any ideas? thanks ....