I've heard that men react to pregnancy a lot differently than women. Our nesting instinct kicks in and we start planning and getting excited, then we feel hurt when it seems like the dad "isn't bothered".
Maybe he's feeling scared now it's finally sinking in that he's going to be a dad for the rest of his life. I don't think men have a lot of people they feel they can really talk to about their feelings. So the one person they might talk to about their feelings -you-, they might not want to go to with their worries and fears, because they feel they'll upset you.
Plus you're pregnant! I expect your hormones and emotions will be EVERYWHERE.
All you can do is sit him down and ask him if he is okay. Make him a promise beforehand that anything he says you won't blow up at him for, and let him talk if he needs to. Just make it clear that you really really need him to be there for you too, and that you need to stick together.
Long story short, maybe you are overreacting a little because of hormones or his lack of excitement now or whatever reason, and maybe he isn't opening up to you as much as he should be. All you can do is talk it out with him and just try to stay calm.
Good luck! xxx