Th kid needs the eprt care of a urologist. If you guys let it continue so that he cant fully empty his bldder, thats bad. Ill bet hes in pain and , as a kid, doesnt know enough to understand the serious consequences you are ignoring.
Have you family doctor refer you to a urologist whose expertise is kids bladder nd prostate problems. It could be as simple as a urethral wound from a sports accident, to stuff more serious.
I hope youve taken the previous advice and are already at the doctors. This should not be ignored or even seeking advice from we "patients"