Young first time mom- please help

My daughter is 2 months old today and she keeps having to go to weight checks. She is gaining some weight, but not enough.

Here’s what I do: breast feed every 2 hours, both breast usually 15-20 minutes on each breast. By the second weight check the pediatrician told me to supplement with formula in the evenings. She will drink enfamil the regular one but she spits up A LOT. so the doctor put her on a medicine e that reduces acid reflux. She fights me with a bottle, most of the time won’t take one. Won’t taker her formula, I feel like I’ve tried everything and do everything I’m supposed to and still, nothing. Does anyone have any advice for how to get a baby to gain weight?