It sounds like you have prostatitis-This is inflammation of the prostate that is from bacteria. It is common to have urinary burning at the tip of the penis. It requires a 6 week course of certain antibiotics such as doxycycline and celebrex to help suppress the inflammation. The urine tests are often negative for bacteria because the bacteria are in the prostate, not the urine.
Best of luck,
The antibiotics will help immediately but are given for 6 weeks to eradicate bacteria in the prostate. They require a prescription.