Newborn only taking 1oz at a time :(

Hello! Wondering if anyone has any advice for me!! My little girl was born May 17 at 36w5d. The pediatrician told us she should be eating 2 oz every 2 hours or 3 oz every 3 hours so she can put on a little weight.

As of right now, at most feedings she will only take 1 oz before she falls asleep/lets me very much know that she is done. Anyone have any thoughts as to why?? Sometimes- but not often she will take 2.

We are doing strictly formula because of a medicine that I need to be on that can pass through my breastmilk. We are currently using similac.

Any suggestions or advice would be helpful to us first time parents!! 💖💖💖