Congratulations for your new baby!
Maybe this baby needs more milk than the others did, so your milk production is up, which would mean you would need more calories than you would have with the others... That's all I can think.
Also, you didn't say whether you pumped with the other two. I pumped for one baby and not for the other, and found that my milk supply (ie, my need for calories) was much greater when I pumped than when I didn't. In fact, when I stopped pumping for a week-long vacation, figuring that my nursing baby would take the equivalent of what I would have pumped, I actually started drying up and the weaning process began. My baby was 12 months old though, so it was okay, but that was when I realized that the amount that I pumped was not equal to the amount that my baby normally drank. Which explains why I had a freezer full of liquid gold!