What Causes Contraction Of Testicles During Ejaculation?

after my husband ejaculates his testes pull up in. he gets urge to cough and they drop but it is extremely painful at times. he is 49 years old and we have a very active sex life. this has been going on over 6 months now and now he is ready to do something about it. what could be causing this and whom should we see to be treated for it?