Sex issue

Ladies I need some help, ideas, input, advice. My husband and I are very actively trying to conceive. We have been making love all week and last night at the peak of my fertile window he could not finish. Going at it for a long time and nothing. I kind of felt like I was the cause of him not being a le to finish be he told me it wasn't anything wrong with me. He has never had this issue before. Nothing I did, orally, on top nothing could get him to that point. Could it be that he is overworked after all week, everyday having sex?