What is it with....?

I really feel for you, you've got to let him know what you're going through and perhaps he may understand

He says he understands, but it still doesn't change anything.

There's your problem. Men like to be the chasers, don't even try to get his attention, let him go for it. he needs the chance to be a man. he probably got a little embarrssed when you complained about the sex. Let him get back to his self, he is entitled to a little time, since all these changes have occured.

How long does this slump last?

Well, it depends. You are loosing self esteem and trying harder and harder. A man responds to this with even more lack of interest. You should never question you attractiveness. Dress nice be sexy, and don't give that man the time of day. He will quikly pick up on this. I don't mean be cold, just be as uninterest in him as he has been to you. I would say it can last for up to a year, but if you make him think on it, he'll come around. Go out somewhere where he has the opportunity to see other guys checking you out.

Thanks for the advice, I'll try not to take it so personally.

God luck, and don't obsess over it, you've got a baby and a new life,
one change makes alot of other changes, and i'm sure as long as the two of you love each other you'll work it out.

I think it just sounds like he's tired, perhaps to the point of mild depression.