Baby weight gain???

So my daughter was 8lbs 10oz when she was born and got up to 11lbs 10oz by her two month check up. She is four months now and I assumed that she would continue gaining that much, seeing as she was still nursing really well and acting very satisfied after each nursing session. I nurse her on demand. But at her four month she was only 12lbs 10oz. I nursed her at the doctor’s office because she got hungry and then I weighed her again and she got a good 3oz. So I know she’s getting the milk.

The things I’m thinking are maybe it was because I had strep (and therefore didn’t eat as much as I normally would) the week before her doctor’s appointment

or

because I have been trying to eat better foods (not restricting my calories or anything, not dieting) with less fats. Could either of those things have contributed?

I know she’s fine because she’s honestly the happiest baby all the time and really is satisfied after nursing every single time. But I just have some anxiety about it all because my son (2.5 yo) wasn’t able to breastfeed.