What Causes Burning Of Penis After Intercourse?

Hi my name is francis, and I will like to know what's wrong with me because I'm scared of that, last nigth me and my girlfriend have sex and after that my pines was like burn and to day in the morning I found out that there's something on the head of my pines like I haven't clean my pines and I was traying to take that of but it just burn a litle