Testicular pain can be a difficult symptom to trace down. It can be related to a hernia, a
sprainSprains involving the abdominal muscles, a
varicocele or a structure within the scrotum such as a rapidly enlarging spermatocele, rarely a testis tumor, residual from mumps orchitis (testis inflammation from mumps in the past), to give you a few, but certainly not an exhaustive, list of possibilities. It is certainly difficult to advise you without examining you but a varicocele sounds to be a likely possibility. An inguinal and scrotal ultrasound with maneuvers to increase abdominal pressure should be diagnostic of this and may reveal other local findings that may help to nail down the cause. You may experience some improvement/relief by wearing a scrotal support if you are not already doing so when you play sports/work-out and wear jockey type underwear day to day.
S.A.Liroff, M.D.