Some kind of rash on my... Uh... "head", help?!

A couple hours ago, like 2 or 3, I noticed the tip of my pe*** was like, a lot more sensitive than usual, in an uncomfortable way, as if sandpaper was gently brushed on it with every touch, now I decided to look, there is a red rash on the head, not all around but just the part facing up, I've had this feeling before for a day at the most but I didn't notice a rash, is it an STI? :/ I haven't had sex yet but I have had an hj... What could this be? :( please help. And if I can't ask this here mind giving me a site that I can post this on?