Have you tried using gas drops? The come sold as Mylicon commonly, but the ingredient is simethicone.
Kelsey would grunt and groan all night, but usually while she was asleep. She would pull her legs up and wiggle. The nurse told us to give her the drops before/after each feeding, and as needed, before bed. It greatly helped. She still gets a drop in each bottle to cut down on the foam/bubbles in the bottle and prevent gas. I also gave them when I was bf.