What Causes Increasing Itching And Redness In Penis After Sex?

Hi, my penis are very itchy recently after having sex with my girlfriend. I never have any precaution and never wash and sleep straight after that. On the second day, it starts to feel very itch and on the third-fourth day, the dick head turn red and even more itch. Sometime it will discharge a bit of clear "water" out from my penis. Can i know what had happened to me? I really very worry. PLs help.