Breast milk not filling up 9 day old

So at my baby 1 week check up with pediatrician she wasn’t getting enough food so he asked for me supplement an ounce of formula once she was done eating, she wasn’t pooping and her bilirubin levels were high. 2 days later her levels have lowered but pediatrician asked that I still pump to see how much she is getting and still supplement an ounce of formula. I’m only able to pump 1-1.5 ounces at a time. So she is getting anywhere between 2-2.5 ounces with the supplemented formula. Somehow I pumped 2.5 ounces, I think it was a fluke cause it hasn’t happened since, and I gave her that this morning and no supplement since she normally gets 2.5 ounces but she woke up an hour later hungry again. I know formula is heavier than breast milk but is it possible that I’m not providing enough for her?