Little or no semen

I had a good sex life until my wife became ill four years ago.  The first two years of her illness I just didn't have any kind of sex. The last two years I masterbated about twice a month.  She is better now and we've resumed a great sex life but unlike four years ago I have very little and sometimes no semen at all. Even in the beginning when we resumed our sex life there was little or non.  I do have orgasms every time... just no semen.  No blood, no pain, no swelling. I have no trouble getting an erection.   I am 53 yrs old.   Could it be that I'm four years older or that I went those two years with no sex?   I do not have any health problems other than being a little overweight.  My urine is not cloudy after sex... I have no other symptoms at all other than no or very little ejackulate.
Thanks for any advice...