Formula

Okay so my daughter just got switched from breastmilk to formula bc of acid reflux issues. She was already not so good eater but now i cant get her to eat hardly at all. I have to give her 2 oz at a time bc it takes her every bit of an hour to finish that. She is 7 weeks old. She hasnt pooped sincw i started ths formula either so i have been giving her gas drops also. It is now day 4. Any advice?