My boyfriend wants a baby.

He has told me multiple times now he wants me to get pregnant and for me to carry his child, and whilst I would love to have children with him, I can't. 
I know I can't, we're both 16, and whilst we are mature, neither of us are financially stable and live with our parents. 
But he is not making this easy for me. 
I have PCOS, so with my hormones encouraging me to try for a baby, and him telling me how he would be extatic, I am in a mental battle with myself. 
I want to wait until we are financially stable and are married, but everything  in me is encouraging me to have a baby. 
I have kittens, I've had puppies, I've had younger siblings, nothing helps. 
I want my own child, and it's making me crazy. I don't want to be a mum yet, and I know it's not likely going to happen as I ovulate maybe twice a year, but it's not stopping my body from going into a mass fever of maternal instincts. 
Help? 
What can I do?