What Causes Redness In The Penis?

Hi, I have a red ness on my penis the first time that this has happen i was on vacation and noticed it so i washed with soap and water every time i showered and it started to fade away i came home from vacation and i play soccer so iam wearing compression shorts and sweating and running around well the other day i noticed the redness starting to re occur and than it began to crust over, I have had unprotected sex only after i figure out everything is fine, iam 19 and iam concerned about this being herpes or any other STD, i tried to do some research but it seems i freak myself out, i narrowed it down to a possiblity to a jock itch but when i looked at the pictures that didnt seem revelvant.. please help