Sex& pregnant

For some reason, every time my partner and I get in the mood he never stays hard when it's time to actually have sex. Ever since we found out I'm pregnant our sex life is non existent, he says it's because he always has a lot on his mind that takes away from him staying hard but I'm just frustrated because it's been over a month. I'm trying to figure out if anyone else has had this problem,? This really is passed the point of frustration.