Infection is the most likely cause. This can include various STDs such as gonorrhea and chlamydia as well as various UTIs.
A urethral swab is not always necessary for culture. Gonorrhea and chlamydia can be tested via a simple urine sample. A urinalysis should also be obtained to look for other causes of a UTI.
If the tests are non-revealing, a digital rectal exam can be done to evaluate for prostatitis.
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.
kevinmd_b