What Causes Burning Sensation In The Penis While Urinating And Masturbation?

So I have some type of scaring that runs down the Middle of my scrotum to the head of my penis... I ve had it since I was at least 10. I m 19 now.. I also have occasional burning after I masturbate or before I pee.. I ve gotten the courage to go to the doctor and had my urine checked. I came back negative for A uti and a few stds.. I m trying to figure this out..