Newborn tummies are tiny y'all. Anatomically, they are the size of a cherry at birth. Because of this, they cannot and should not take in large volumes. Aka - babies need to feed frequently. In the first day or two, their little tummy will fill with anywhere between 2-20 ml during a feeding. This is when your body is producing good old colostrum. A drop of this liquid gold really does go a long way.
In addition, newborns often cluster-feed. Meaning, your little one may breastfeed for 45 minutes then fall asleep, then wake 30 minutes later, feed for another 30 minutes, and then fall asleep again. The next feed may happen 2 hours later, then again in an hour. There is no set schedule. Feeding on demand like this is the best way to establish a healthy milk supply.
Many families feel the need to supplement early on. I truly think that some of this stems from the frequent feedings. Cue the concerns - are they getting enough? Do I have enough milk? How can they be hungry again? But, understanding the size of your baby's stomach, the average volume taken in during a breastfeed, and typical newborn feeding frequency can help alleviate some of this anxiety.
Decreasing anxiety through informational and educational support allows you to trust in your body's ability to nourish your baby. Newborns are only this tiny for a short time. And those stomachs grow quickly! By one month old, it will have grown to the size of a large egg. In time, breastfeeding sessions will become less frequent and shorter. You're doing great, I promise!