EBF premie

How do I know she’s getting enough milk?? She’s almost 5 weeks old but 38+2 gestation. I can hear her gulping in the very beginning when I have my let down but I don’t hear much gulping after that! I see milk dribbled from her mouth when I pull her off to burp her. She’s having plenty of wet diapers. Sometimes she still seems hungry though after feeding for like 35 minutes total on both sides. Then I’ll pump after because they still feel slightly full and I get a similar amount of milk I would get if I didn’t feed her before I pumped which is around 3oz. I’m just not sure 🤔 also I have to use a nipple shield because I have flat nipples so I’m not sure if that messes with milk transfer??