I sometimes have this burning stingy feeling in my penis and when i ejaculate my semen is really runny and watery when normally its thick and shoots out instead of flowing out like water. When this happens i have a lot of pre c-um while i masturbate. I'm soaked in it and then i cant ejaculate properly and after ejaculation i feel a burning sensation.But after a few days it goes away and everything is normal for another few days but then it comes back.I'm still a virgin so it cant be STD'S.What can this be?