Even if the prostate has been evaluated, that would be the most likely cause. I would consider imaging the prostate (i.e. with a transrectal ultrasound) to look for abscess.
If the prostate is completely normal, I would still consider a cystoscopy to evaluate the lower GU tract. However, I do not have the benefit of examining you, so your urologists may be seeing something that I'm missing.
Another opinion can be obtained - preferably at a major academic medical center.
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.
kevinmd_b