Hello, I'm 32 years old. I self please myself, 2-3 a day. I notice from time to time, I would have my tip of my pee hole hurts. It feels like, a light burning of the tip of my penis. I got tested for Chlamydia,Gonorrhea and for Urethritis. All of them came out negative. I only have one partner. Every now and then, when I masturbate 2-3 a day. I would have a burning feeling at the tip of my male pee hole. My bladder doesn't hurt, no complication of releasing urine, no blood in urine and no swelling. What can this be ?