Can I gently ask about your eating habits prior to conceiving?
In my past three pregnancies, I had a very disordered eating pattern before pregnancy(ies). I'd skip a lot of meals, eat dinner, eat too many snacks late at night to compensate for not eating all day. Or I'd binge eat for a while, go back to eating sparingly, etc. All of that to say, it really messed with my metabolism.
Any time I'd get pregnant I would force myself to eat like a normal human being. I wouldn't even eat to excess, but the immediate shift in eating pattern did a number on my body because my body was so used to never knowing where or how the next meal would come. I packed on the weight in my previous pregnancies, but if you saw my meals you would wonder why I was the one putting on so much. Of course I'd indulge but never repeatedly.
With this pregnancy I had a much more stable eating pattern prior to falling pregnant and I've maintained the same schedule for the most part throughout the past few months, so my weight gain has been MUCH more subtle than the others have been.
I may be totally off base, but I figured it was worth mentioning because I know I'm not alone in having very off eating habits.