Hello epididymitis, or inflammation of the testicles due to STI, untreated testicular torsion or trauma. a hydrocele, which is characterized by swelling of the scrotum, an inguinal hernia, all can cause pain, if there are no causes found then,, wearing '-shaped underwear, high upto waist so that your both testis are lifted up helps. Eat more of fresh fruits and vegetables, if pain increases , please consult general surgeon.