If these symptoms have been on and off since his vasectomy, he may have a sperm granuloma (chronic reaction against "spilled" sperm in the surrounding tissues) or congestive epididymitis. This would be treated with anti-inflammatories like Ibuprofen, or sometimes may require surgery to "vent" the swollen epididimys.

Here's an article on complications of vasectomy:
http://findarticles.com/p/articles/mi_m3225/is_n7_v48/ai_14674604/pg_3

A urologist would be the person to see.

Ellie