Testicular Pain

[Rouge]

Hi!

I'm not male, but my partner is (and is off with the forces) so I'm posting for him.

For the past few months he's had on and off pain in one of his testicles. He's been to a Urologist, but they found nothing. He has an appointment scheduled for when he returns with another one, but where we are right now is very small, and I doubt that much has been seen. He says that he notices the pain intensifying if he masturbates more than usual, or if we've been having a lot of sex.

What could be the causes of this pain?

As well, he's been on three rounds of antibiotics (different ones), but it still returns.