Please help

Hi everyone, I’m at my wits end. Baby was born December 13 and is now above her birth weight. I’ve been breast feeding her and things have been ok so far but lately she just feeds for 10-14 minutes and stops. She either falls asleep and no matter what I do i can’t wake her or she just stops. I’ve read and been told that each feeding session has to be at least 30 - 40 minutes and I’m so worried she’s not getting enough nutrients 😞