Grunting and discomfort during nursing

My almost 4 month old has started grunting and moaning while nursing. He doesn’t unlatch but pulls away. It’s been a few days. Idk why he’s doing it? Maybe my supply is dropping? I’m always worried he’s not getting enough and don’t want him to be hungry. He’s had issues with spitting up and gas. I went dairy free and it’s helped a lot until this started. Any ideas? Feels like he’s trying to rip my nipple off 😆 and idk how much more i can take.