Prostate could be correct. A hernia can also be suspected. Do you feel any protrusions in the scrotum when you cough? Any swelling in that area? To rule out the prostate, is there any difficulty with urination? frequent urination? An urge to urinate but inability to go? Blood in the urine? I would suspect a hernia if you recently did heavy lifting, overstrained your back on a lift, etc.
To check for a hernia, feel knida behind your testicle and first bear down like your trying to fart, then give a good cough. If you feel like a protrusion pushing against your fingertips when you do this, you gotta hernia bro. PM me if you got any other questions bro