Hello, I Am A 56 Year Old Man Who For

Hello, I am a 56 year old man who for the last 6 months or so has seen a sudden sharp reduction in the amount of ejaculate. The feeling during orgasm is of the ejaculate being forced, not exactly painful but not as pleasurable as it was beforehand either. Sometimes there is not only very little semen, but it trickles out as being delayed physically. Although I having read up on the subject of virility in ageing men and the expect decline in the amount of semen/sperm produced beyond a certain age, I still find the suddenness and the amount of the decline alarming. I am in reasonable physical health as far as I know and can't account why this should happen. Can you asses this based on the information given and suggest what may cause this please?