When does intake increase?

My baby is 5m old. She has been drinking 4oz at daycare every 3hrs since 3m. She doesn't act hungry after she's done, and still spits up quite a bit at times. My question is, what age would baby typically start consuming more milk? Or will she? I've read conflicting things, that your milk changes and they will never need an increase in the amount....and also read after 6m. We have not introduced foods yet, and probably won't until she shows signs of being ready (my guess is 7m+, she's a preemie). Thanks, ftm & EBF!