What Causes A Red Colour Rash On My Penis Tip?

hello doctor,i am 24 year old,about 4 years ago i had sex with a prostitute and few days after that a red coloured rash devloped on the edge of my penis cap,i had a burning feeling if it was touched,it started drying up and disappeared after about 2-3 days,i haven't devloped any symptoms after that,but sometimes after masturbation the same area becomes red.do u think i have a sexually transmitted disease.please advice.