Husband unable to perform

so this is ovulation week for me, but for the past two nights my husband has lost his erection in the middle of sex! We’ve been together almost 5 years and it’s never happened before. We’ve been ttc for four months now. He works second shift as a cop and has come straight home changed his clothes and headed upstairs to wake me up. I tried to talk to him about it, but I just upset him and he thinks I’m mad at him now! I think last night was really the issue and he psyched himself out for it tonight, but what can I do to help him over this? Yesterday was the big O day, but he did get another erection and we did it again with no problems, but not so much this time!