No more sex?

Ja
My Boyfriend and I have been dating about 3 1/2 years now. We moved in together 7 months ago and now have a 3 month old baby. We didn't have much sex while I was pregnant and I was excited to get things going again after he was born. We used to have sex daily but now we're lucky to have sex once a week. I always have to beg him for it too, he always insists he's too tired or doesn't feel like it. The occasional sex that we do have now just isn't the same. HELP!