Male. pain in the groin (like blue-balls) for 3 weeks, it feels like i have a 3rd testicle on the right side. why so long? would masterbaition help?

Probably not: This is not likely due to testicular engorgement (i.e. "blue balls"), such that ejaculation will lead to reduction in swelling. Instead, this is more likely either be an inguinal hernia or hydrocoele. You should have your physician check this out. If the pain worsens, you should seek attention, as the diagnosis of testicular torsion or epididymitis may need to be ruled out.