Basically me and my partner have been together 5 years and we have a baby together and I’m pregnant we love each other and we work well as a family

But .......

Here is the thing he never initiates sex if I start it he gets in the mood and it’s great but it bothers me that he never initiates sex

I feel so unwanted when I talk to him about it he says he don’t know why and that he just don’t

Has anybody been through this or got any advice on what could be wrong ???