Prostate problems first come to mind, but your urologist discounts that. You can further evaluate with a transrectal ultrasound to be sure.
Infections of the lower urinary tract can also be ruled out - with a urethral culture and analysis of the urine.
Anatomical abnormalities, like a urethral stricture or urethral polyp can uncommonly cause similar symptoms. A cystoscopy can help with the evaluation.
These options can be discussed with your personal physician, or in conjunction with your urologist.
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.
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