Having a baby is a big change in the dynamics of a relationship, and frankly, I don't know many women at all that want sex after pushing that thing out, lol. I sure didn't, after either of my children. There are a lot of reasons for that, the biggest is that your body needs to recover, but also you are probably tired from caring for the baby and if your SO is like most guys then he isn't helping much.
I'm no expert, my SO became pretty abusive after each of my children was born, physically after my second. He liked to pressure me into sex, and sometimes I would give in for the sake of peace. Thing is, if he had been nice to me, helpful and understanding, and willing to wait for me instead of pressuring me, by about 3 months after delivery I would have been ready. For me, that was not to be.
I would probably suggest asking mom to watch the baby some night and sitting down with SO and discussing things the way you see them. Much better to be open about how you feel then to have things implode because of deep misunderstandings, but if he feels like you do, just remember that the baby isn't a good reason to stay together.
Dez