feeding Constantly?

My 8 day old baby girl wants to do nothing but feed. I am feeding and haven't given her a pacifier at all. She will eat, fall asleep for a wee bit and as soon as she is awake again wants to eat. I know I am producing mild as I can hear her swallowing, I am also easily able to hand express milk. I am worried that maybe she just isn't getting enough. Also once she actually falls asleep she will sleep for 3 or 4 hours. Is this common?