Husband's low sex drive issue when TTC

I do hope someone can give me an advise on how to handle this issue. My husband and I have been TTC for a year now. We had an amazing sex life before we decided to start family. But it seems like the very next day we put an agenda on our sex life, everything changed. If I tell him the weeks I am ovulating, he becomes unable to get it up. If I don't tell him, the days we get busy on don't normally click with my pick times. I am 35 years old and this has become extremely frustrating to me and put a big burden in our marriage. Any advise???