Can masturbation cause epididymitis? If not, then how can masturbation cause testicular pain? I have chronic pain from time to time. Only right side.

Not epididymitis. Masturbation cannot cause epididymitis. Frequent ejaculations can cause pelvic pain or discomfort that can be perceived in the testicles ("blue balls"), but that's not likely to involve only one testicle. Try laying off masturbation several days and see if it makes a difference. If not or still concerned, see your doctor.