Hi,
Scrotal swelling is abnormal enlargement of the scrotum, the sac surrounding the testicles.Scrotal swelling can occur in males of any age and may or may not be accompanied by pain. It can occur on one or both sides. The testicles and penis may or may not be involved.
A testicle lump is a swelling or mass in one or both testicles. testicular lump that doesn't hurt may be a sign of cancer. Most cases of testicular cancer occur when men are between ages 15 and 40, although it can happen at older or younger ages.
Some possible causes if the testicle is not painful, as is in your case could be ,Hydrocele (fluid collection in the scrotum) ,Varicocele,Spermatocele or loop of bowel from a hernia.
ref:http://adam.about.com/encyclopedia/Testicle-lump.htm?once=true&
You should see a doctor and get the swelling examined. Diagnostic tests and treatment can be decided only after that.
Only a physician can tell you but PLEASE get checked out right away. Testicular cancer stikes young men in your age bracket but is VERY treatable is caught early.....