We've been at it for a year and a month, weighing 8.7-8.8. She feels g…

We've been at it for a year and a month, weighing 8.7-8.8. She feels good, is very active, seems to eat normally. But we can't gain weight. And I and my husband are thin and tall. She's tall, but is that normal in our case? Or is it still underweight? The pediatrician said she's skinny. We barely manage to gain weight. Two months ago, she weighed 8.6, and in this time gained only 100-150 grams ? By the way, she hasn't started walking yet, maybe because of this all the gained weight gets burned off when she crawls? How much did