Low Libido

Ever since having my daughter 18 months ago, my sex drive has decreased so much. My fiancé and I used to have sex pretty much twice a day every day. After having my daughter the minimum we have sex is once a week and the max is probably 3 times a week because my sex drive has lowered so much. Now i’m 16 weeks pregnant with our second and my sex drive is still the same. This has left my fiancé extremely sexually frustrated all the time and I have no idea what to do. He ends up asking if I even find him sexually attractive anymore or if i’m going to cheat on him and says things like i’m the only person he can have sex with so that’s why he’s so frustrated. He feels like we always have sex when I want to but he always feels rejected because he wants to have sex all the time but I can’t do that. I just don’t have that strong desire to have sex all the time like I used to. When I want to have sex he always wants to but if he didn’t then of course we wouldn’t have sex same as when I don’t want to or i’m too sick from the pregnancy or too exhausted. I also have times when he wants to have sex but my mind is stuck on all the millions of things I need to do and I can’t get in the mood to have sex. Any suggestions? Anything I can take to up my drive or something he can take to lower his?