Not enough weight gain and nursing?

So my LO is 5mo and during a recent appointment this week, doctor said she’s falling a bit off her curve. Basically she hasn’t gained enough weight since her last weight check. I’m exclusively nursing. I tried pumping afterwards and it wasn’t even 1oz. Have I lost my supply or slowing losing? I feel like she’s eating the same amount. I feed her usually twice in a wake window or whenever she crying. She’s going through a sleep regression, waking up almost hourly to nurse back to sleep (we’re working on that separately). She hasn’t gained enough pee diapers and poop diapers throughout the day. Doctor suggested to top up … but she refuses the bottle (pumped or formula)! She also has CMPA so the formula we do have for her is kinda bad tasting so I’m not surprised.

Any advice or insight?