Baby sleeping 20-21 hours a day. Help please!

Hi everyone, I gave birth at 39+4. My baby girl is a week old and still sleeping 21 hours a day. I am getting very concerned. She has to be waken up for feeds but even then she would have her eyes closed. She is for sure getting enough milk, which came in by the second day of her born. Her latch is ok too. She does not have jaundice, her temp, breath count is all good. She has two very noisy siblings so it is not like the house is a tranquil environment to sleep in. Has anyone else had a baby like her without medical concerns or found out why this is happens? Any ideas and experiences welcome. X