Not feeding enough?

Brit • Blessings to all women TTC & giving birth. Married to my bestfriend, we have a beautiful 4 year old daughter & 5 months pregnant with our boy 🦋
My girl was born at 7lbs 13oz due to a stressful birth and being VERY swollen. Discharge weight was 7lbs 7oz. We went to the pediatrician for the first time last Friday and he said weighing at 7lbs 4oz she is very underweight and I am not feeding her enough.
I explained to him that she eats mostly every two hours, 2oz per feedings. She sleeps a lot and there are times she will pass a feeding, but that'll only be her sleeping for about 4 hours at the most. She eats 2oz after waking up and even trying to feed her a bit more has failed. She sleeps so much, but I see nothing wrong. She is happy, not fussy, and she doesn't want the bottle as much as I want her to eat more!!
I tried waking her up these past two days like he said but every time I have woken her up she has just spit out the bottle with a nasty look on her face. She's very uninterested in it, until she's hungry. Everything else in her is healthy. 
Could this just be a case where my baby is a little different compared to the charts?? We go in again tomorrow morning for him to check her weight if she had gained these past two days (which I doubt) and if she hasn't then he is giving her an ultrasound to see if there is a problem inside. I'm nervous!! 😢
If it helps, we have been giving her similac like the one they provided in the hospital, and as much as I can, giving her my breastmilk!