Difficult to say without examination.
Infection continues to be a leading possibility despite the lack of other symptoms. A urine test, urethral swab, or prostate exam/massage can be done.
Imaging the penis via a cystoscopy can be considered to exclude anatomical possibilities.
I would suggest a urology referral at this point.
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.
www.kevinmd.com