Infection still would be the most likely cause of the symptoms. Even if the tests for STDs (gonorrhea or chlamydia) are negative, I would still send the urine out for culture.
I would also test the prostate for infection - which can be done via a digital rectal examination and expression of prostatic fluid. Your personal physician or urologist should be able to do this. If negative, a transrectal ultrasound can be considered to evaluate for any prostatic abscesses. Prostate infections can be very difficult to treat, sometimes requiring 4-12 weeks of antibiotics.
You can discuss these options with your personal physician.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
Medical Weblog:
kevinmd_b