IMO there is some good advice in here, and every relationship is different so it will be up to you and your wife what might work for you from people's suggestions and what won't.
My two cents - it's most likely related to pregnancy and hormones. If I can go ahead and make some assumptions based on my own experience: She's exhausted (seriously, doesn't matter how far along she is, she's exhausted), she's worried about baby #2 and how much work that's going to be (for both of you, but particularly the load will be on her for the next while depending the feeding situation), and while it does sound like you do a lot to help out with the family and around the house, sometimes "being supportive" does not just equal "doing your share of chores". She's (I'm assuming) hormonal and wants to feel loved and appreciated. Well, maybe feeling loved and appreciated is what every person in a relationship wants, but this definitely seems to be magnified due to the crazy pregnancy hormones from what I can tell.
Good luck, and I'm sure you guys can work out a compromise so you're both satisfied!