Constant testicle pain

My boyfriend, has been having trouble with his male nut area for quite some time. He had surgery when he was 12 years old because his nuts had twisted together. He has had terrible pains in that area. The pain varies from sharp, to dull and then back to sharp and nagging. It hurts to sit down, it hurts to walk, and to stand. It hurts him to cum, and after wise hurts also. He barley cums, and if he does it is very little. What could this be? He is now 29 years old, that is several years with this pain. Thank you.