Explain to him how hard it will be to have 2 baby's at the same time. How much they cost, formula,diapers,clothes,if they get sick etc...Does he have a job? Tell him that you want them to be at least 2 years apart but that you def want another baby. He should understand. You guys are both in this and like you said its your body and you just gave birth 3 months ago. You need time to really heal all that.
I hope he understands where you're coming from cause I really dont want you to do something you'll regret later on.