Dull, heavy ache in scrotum or testicles. it doesn't hurt it's just an annoying ache. what could this be? i've had it for months now.

See a urologist: It is possible that you may have a varicocele. In plain English varicose veins of the venous plexus of the scrotum. Most often on the left side. Treated primarily with surgery. You need treatment if you want to have kids, because the extra blood flow tends to increase the temperature and decrease sperm production. Testicles are outside the body in a sac because the temperature is lower.