Suggest Remedy For Lack Of Semen During Ejaculation

My husband has no histroy of prostate problems, no testicular pain or swelling. He has a history of back problems, slight scoliosis, and takes synthroid for his thyroid problem. In the past month, he has been having orgasms with no fluid release, and I am concerned that this will affect his fertility. Could this just be a simple problem that medication can fix, or should I be worried?