I Have A Pain In My Urethra Every Now And

I have a pain in my urethra every now and then. I used to have a milky whit discharge but it has stopped but the pain is still there and I have an unusual feeling in my urethra when I ejaculate. It's up around the head of my penis. It doesn't hurt all the time or burn when I urinate. I have ben tested for gonorrhea and chlamydia but the results were negative. What could this be ?!