It is assumed that testing and treatment for STDs as well as a urinalysis have already been performed.
You can consider a prostate infection - which can be evaluated with a prostatic massage (and sending any fluid off for analysis and culture). Most cases of prostatic infection requires several months of antibiotic therapy.
If all infection has been ruled out, you can consider a cystoscopy to evaluate for anatomical abnormalities - such as a urethral stricture or polyp.
These options can be discussed 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.
http://www.straightfromthedoc.com