Well If it was unexpected it can be a big stresser. He can still be happy about it but in a panic mode If he doesnt know what to do about it. If this is the first child for both of you its a big life change and you have lots to plan and prepare to, the importan thing now is to talk alot and for you to be there and support him as he should be to you.

28 pounds in 3 weeks ? does he eat like a bodybuilder without the bodybuilding ???

He knows you're going to get fat, so he's just getting a head start.

sympathy eating. getting a head start on your "weird cravings" phase. but seriously, sit him down and talk to him about it.

Could be a couvade syndrome. Nothing to really worry about, it will stop on its own at some point.