What Causes Throbbing Pain In Testicle?

hi doc my partner has been complaining of a slightly uncomfortable throbbing left testicle, i am concernd it could be a sexual infection or earlie signs of prostate cancer, it comes and goes he said the throbbing doesnt hurt to the point of having to sit down or anything but he says its a bearable pain. i asked him to see a docter but he keeps avoiding the issue i was hoping you had any slight ideas of what it could be ?