My husband has enlarged testicle.

My husband's told me last night that his left testicle is about 2xs the size of the right one. I felt it & agree that it is larger than the other one. He says that it is slightly painful at times and has been this way for a few months. We were intimate last night & he was fine at first. I wanted to be intimate again about 2 hours later, but he said it had been hurting him for the last hour & a half. It was not something he was up to. I am hoping someone out there might have an idea of what could be wrong with him. He has not gone to a dr. & says he will when he has the time. I believe he should see a dr. sooner than later. Hoping to hear from someone so that I can show him the information & hope it will motivate him to see the dr. sooner.