Hi, There can be an infection in the scrotum which is causing the pain. This can mean an infection in the testis and epididymis. The surest sigh of such an infection is pain relief and feeling comfortable on lying down and lifting the scrotum with your hands. To confirm an infection requires consultation with a surgeon. If a single diagnosis cannot be found after clinical examination then an ultrasound scan of scrotum has to be done. This will show and features of infection, abnormal blood flow or collection of fluids as found in hydrocele. If it happened few days back then it is most likely and infection. Such infections can be treated by medications. A complete course of antibiotics and pain killers might help. Please avoid doing heavy physical exercises and going to the gym for a week.