My testicles always hurt when i have a boner after masturbation. the pain fades when boner is gone. i don't put pressure on testicles what's that?

You may have been: too vigorous with your masturbation technique, or you may be subjecting the area to masturbation too often. Having an erection requires hormone and circulation, both of which are affected directly by what your testicles produce. Ejaculation also depends on glands that sit on top of your testicles which could exert some pressure during function. Try to take some ibuprofen after each episode.