Hi, unfortunately this reaction is all too common. Post Vasectomy Pain Syndrome (PSVP)is a very real and well recognised phenomena, but one that the medical fraternity plays down. Studies show that between 10-30% of men go on to develop chronic pain, which is not always treatable. MY DH suffers from this 2 years after his Op., and he is having to learn to live with it.
His visits to doctors have been fruitless - most believe their own propaganda that it is a simple 15 minute procedure with no risks. One urlologist my hubby visited did admit its existence, and recommended the removal of the epididymis as a 'cure'.
Did your DH have the procedure done on the NHS by any chance? There is evidence to suggest that procedures carried out privately (Marie Stopes etc) are less problematic as they emply a less envasive no-scalpel (NSV) procedure.
It is likely that your DH's pain comes from either nerve damage from the tugging that often happens during the Op., or the fact that the testicles continue to produce sperm with no escape, (now that the tubes have been sealed). This causes a build up of pressure which often will lessen over time - either because the vas tube expands to accommodate the increased sperm and begins to reabsorb it, or because the pressure will rupture the tube to form a granuloma. A granuloma is a hard build-up of leaked sperm into the scrotum, which may or may not be painful. Around 60% of men experience this as a result of vasectomy.
I realise that this is not a very encouraging post, but is based on my own hard earned experience. As someone who has witnessed the effect of this on my DH, I am trying my best to point out the risks to others so that they can make an informed choice. Please let me know if I can be of any more help.