What Causes Small Bump On Right Testicle?

my 23 year old son has just informed me that he has a tiny bump on his right testicle. I can t get my doctor s office to see him for another month. Should he go to an ER or Urgent Care facility- he doesn t want to and we have an HMO. He says it doesn t hurt but his testicle feels heavy at times. Now he tells me he s had for awhile.