60 y/o male, no sperm for the last 4 months, orgasm burns slightly. No problem with erection

I am a 60 y/o male, and for the last 4 months I do not have ANY sperm.  I get stimulated and can climax however it is dry and burns slightly when I climax. It bothers me to no-end that I have no sperm but have ano problem having an erection.
What can I do?  What might my problem be?  Please offer your opinion!  Thanks!