My Baby Girl Is 4 Days Old Have Been Home

My baby girl is 4 days old have been home for 2days, I breast feed and it seemed to be going well until today. She use to eat for 20-40mins then move her head and go to sleep, today she was being fed and then starts crying I tried switching positions then switching breast nothing seems to be working. I am nervous because she has done this all day and I want to make sure she is getting enough to eat.