21 yrs old, 6 2, 180 lbs, A week from today i had unprotected sex with my girlfriend of 5 years, each day since then I have felt a really vague burning on the tip of my penis , my penis looks normal but on the inside of the tip there is a small red mark; im not sure if this is a bump or just a mark but im worried as to what this could be and what i can take to rid of it