Is baby getting enough?

I'm beginning to think my 11 at old is not getting enough while feeding. About 5-7 minutes into feeding she will squirm and begin to cry, as if she is not getting any milk. She does this on both sides. However, I can pump right after feeding her and get 1-2 ounces from each side so I know there's milk in there. I think she gets frustrated when it doesn't flow freely. Any advice on how to satisfy her, especially in the middle of the night?