Hi. Thanks for your query. The most probable cause of the pain and soreness in the testicles after masturbation can be partial torsion as caused by the vigorous act you may be doing. The abdominal muscles must be getting into spasm making the cremaster muscles to go into spasm and pulling the cord and the testes and causing partial rotation called torsion giving you the sensation of pain . I would advise you to consult the Urologist for : Clinical evaluation and physical examination Ultrasonography of the scrotum and the abdomen to see if you have prostatic congestion or so Stop being harsh. Use scrotal support. Stop masturbation till the proper diagnosis is made and treated.