Facing fatherhood is a daunting experience for many men, even the ones who were totally on board with trying for a child. It suddenly becomes real in a new way, and some begin to wonder about lack of freedom and being buried in new responsibilities. He doesn't have the hormones circulating that you do, bringing warm feelings and a sense of wonder and connection with this new life.
He could be more or less terrified, and not feel that it's okay to express his feelings. It's not uncommon, for men and women in those circumstances, to look for 'coping' behaviors, anything that brings temporary distraction or relief. For some new daddies, they seem even MORE distant after the baby enters the world, because they really have never learned how to interact with a helpless infant.
Do all you can to let him know all the ways you appreciate him. Make a point of 'setting him free' every once in awhile – encouraging him to take some time off for himself. Find ways to include him in the baby's development, without making the next several months all about you and baby. You may seem more preoccupied to him, too, and he might be feeling like an extra wheel right now.
Talk to him about your needs – be careful NOT to complain about what you perceive he's doing wrong, only what YOU need that he can help supply. And don't forget to ask him about HIS needs – this part of the equation doesn't even occur to some pregnant women. Nature is making extraordinary demands on your feelings and your body, but he can't really know what that means (just as you couldn't know before you became pregnant). He can only feel and experience his own needs. That's just life.