Doc says baby isn’t gaining enough?

J

My baby was born 5 weeks early due to cholestasis. He was 5 lbs, 14 oz. he’s 5 weeks old now. The doctor is worried he isn’t gaining enough so he wanted me to start giving him formula. I have, but I really wanted to only breastfeed. Last week he gained 6 oz on just my breastmilk. I thought it was normal to gain anything between 4-7 oz a week? He has plenty of wet and poop diapers. He’s satisfied after a feeding. I’m just scared this may mess up my supply. Any opinions on to why they may think he isn’t gaining enough? Let me also add that we’ve seen a different doctor each week. And one says he’s doing great and another one says no. It goes back and forth 🙄 no doctor says the same exact thing. They are making us come in every week for a weight check even tho he continues to gain weight