Why is she doing this

OK I have a newborn 7 days old and she's feeding 21/2oz every 3 hours, it's all she will take throughout the day but when bed time comes say 1-2am every night she guzzles 4oz and is still asking for more :/ I just don't understand why she's wanting so much between them 2 hours and won't drink that much throughout the day, 8lb 6oz weight was when she was born and I just don't understand like...