I'm thinking that he's not receptive right now because your marriage hasn't been stable... and it's not responsible or appropriate to get pregnant while in a situation like that intentionally. If your hope is to "fix" your marriage with a baby, it will magnify or cover up your problems instead. And it won't be fair to a new baby nor to the children that you already have.
It sounds as if you guys have a history of having trouble communicating. I would strongly suggest marriage counseling and therapy. It's not about telling each other what's wrong and how to fix the other or one person... it's about learning how to communicate and learning skills together to work on the relationship.