Hi After I Masturbate Why Do My Penis Stings At

hi after I masturbate why do my penis stings at the tip I had to go to the doctor about 2 years ago for having sex with this girl and she burned my penis and they gave me a shot in to but then it went away but in a weeks time it came back but i could hardly feel it and I havent gottin treated since 2 years ago but sometimes after i piss i can feel a stinging sensation but it do not hurt that bad like it first did I just asking what you think i maybe have because im scared