Maybe the nipple size is too fast? I know sometimes babies tend to eat to fast that can also cause spit ups. My daughter was doing the same for a little when I’d pump so I also just gave her half of her oz and then tried to burp her and then I’d continue to give her the rest of her bottle. Hope this helps. 🙏

I got Mam bottles and you can hear the air escape. I also bought an elevated pillow bed for him & that helped