Avent bottles

Katherine • Police wife 👮mommy to Benjamin and Jason 💙💙
I'm using the avent bottles for my son. He's just about a month and a half. We still have him on the first flow nipples because he spits up so much and my doctor told me it's not necessary to switch nipple flow. But, every time I feed him he sucks the nipple into the bottle. Every couple sucks. Anyone else experiencing this with avent bottles? And what bottles are you using?