tips on improving sex life

Me and my boyfriend rarely have sex. It's me, not him. For a while, even before I got pregnant (I'm 24 weeks) we barely ever had sex. My sex drive just isn't very high and I have no idea why. We've been together for 3 years and half and use to have it regularly. It's not him, I'm attracted to him, I love him, he pleasures me and cares for me when it comes to sexual intercourse. I know it's getting him down about how often we have it and I feel like it's putting a wall between us. I just want some tips to improve it.