Relationship Advice

So me and my boyfriend have been together for 2 years , we lost our baby girl a few months ago. He drives me insane sometimes. He asks me for sex all the dam time. If I have sex with him a few hours later he'll ask me again which pisses me off. Don't get me wrong I love sex but the way he is with asking for sex all the time is a turn off. If we go out to do something fun or enjoy our time he'll later bring up that we went out together and that I should give him sex for doing what i asked. I asked him today to help me put our new mattress in our room and he just said I helped you, now we have to have sex. It's never an ending to it, I don't want to be having sex because I feel pressured. It always feels like " either we have sex or I won't do this for you " I feel it's unfair. I just want to be able to have sex with him because I want to not because I feel pressured into it. If I tell him no he gets mad if I lie to him so he would stop asking me he gets mad. So I don't know how I could get the point across to him that sex should come from both of us not ultimatums