As a mom of four (so far), I thought I would chime in, so take it for what it's worth. I am also coming from the perspective of a Catholic who doesn't use artificial means of birth control, but contrary to popular belief, I ain't just popping out babies left and right
Dh and I when we were first married thought that two kids would be perfect (after all, that's what society tells you is socially acceptable it seems). When we had our second, we were so thrilled that dh said 'let's have one or two more.' When our third dc was born, he said why not five or six? LOL As I like to say, the equipment is still working, so anything is possible.
The yearning you are having is natural...it's called being a woman! We were made to have babies and love them.
As for your dh, perhaps he is ingrained with the thought that two is socially acceptable and any more would be perceived as weird (I guess that makes us downright insane!). Perhaps he is worried about the monetary aspect of it (dh makes about $54K a year and we raise 4 kids on it, with two in private school even). Perhaps he is worried about being emotionally able to parent more than two--some days it is difficult, but it is amazing how much your love grows when there are four little people wanting attention.
I have a sil who is adamant about having no more kids (she has two girls, ages 6 and 3), and her dh would love one more. It is painful to watch because she is not exactly gentle in her refusal and it is hard for me to not take it personally when she makes comments about there is no reason for her to have more.
I wish I had some wonderful advice, but I don't, because my dh is open to more kids if they come along.