You made this baby together. Your body needs a few months to recover, before you can return to work. He expects you to contribute financially, even when you're not earning, because you are recovering from having his baby. What an absolute Wanker.
Just for giggles, I'd sit him down and tell him that you've decided to go back to work, one week after baby is born. Nurseries won't take newborns, so he will have to take 3 months off work unpaid. You expect him to pay half of all of the bills, when he isn't earning any money. See what he says?
In reality, I'd leave this Arsehole, and go back to your mums. He is financially abusive, and it won't end here. He will no doubt expect you to take on more childcare, thus reducing your earning potential, and still pay half the bills. He may even want you to cover all Nursery bills. This isn't just your baby, it is his as well!
Aldo, as you're not married, you are in an especially vulnerable position (financially).