What Causes Severe Itching In Urethra Post Masturbation?

So I've been having an itch in my uretha for the past few weeks only after I ejaculate. I masturbate a lot and now have slowed down to avoid the itching. I've gone to the doctors and my blood test, and urine test came back negative. I had some blood in my urine, but I think it's because of me compressing my penis and rubbing to scratch the itch.