I have the same problem. The Urologist told me that it is called "retrograde ejaculation". If one does climax the sperm is shot into the Urethra, goes into the bladder and is excreted with the urine. I understand that the evaluation procedure is to check the urine for semen following a climax.
According to the Urologist the medical profession does not know why this happens (absent direct damage to the genitals) or how to fix it. It's apparently a permanent condition. I've searched the Net (a lot) and cannot find any answers.
I'm trying my own experiment which consists of regular Kagel excercises (you don't have to overdo it), masturbating and trying to hold off a climax as long as possible. Lately I have been getting a few drops of pre-cum. It's better than nothing but nothing is better than shooting a big wad. Normal ejaculation is a lot more intense and satisfying.
For everyone's information, mine started after I had major abdominal surgery. It related to my intestines and no surgical procedure was performed anywhere near nerves or anything else that could affect sexual performance. However, I was the hospital a long time and full recovery took about six months. During that time I had zero libido.
Prior to surgery I was producing semen prodigously to the point where the tubes around my left testicle would hurt continuously until I masturbated and released the built up supply which happened a few times a week. When full the tube at the end of the testicle felt like a big knot. Post-surgery I was concerned about my lack of desire, felt around and the tube felt normal with zero build-up even though I had not had sex or even tried.
Something changed. I speculate that the lack of use for a over six month period resulted in the sperm tube rerouting itself. The Urologist doesn't know either but it is a medical fact that the production of semen and sperm does continue to accumulate inside the body. It will be excreted or absorbed. Shooting it into the Urethra is the most direct method of release.
Although the doctor did not know about the theory, I read in several articles that ED can be one of the lesser known side effects of abdominal surgery but no one knows why.
See if you can trace it back to some event such as a bladder infection, epidetimitis, an injury (no matter how minor) or something else. One fact I did learn is that if your testicles or the cords inside the scrotum hurt go see the doctor immediately even though you might feel like a wuzzy doing it. If the cord carrying blood to a testicle becomes kinked or otherwise closed off the testicle dies and must be removed.