Baby throws up after bottle feeding.

Sog 🎀
So my baby is one week old today.  I've been trying to breastfeed on demand but she isnt gaining as much weight as the Dr would like to.. So in addition, I pump and feed her my milk using Dr. Brown bottles.   Everytime I use a bottle, she throws up some of it even after I burp her.. She does not throw up at all after I breastfeed.  Has anyone experienced a similar situation?   Any advide is appreciated.