Newborn sleeping too much?

My 9 day old newborn went to the doctor's yesterday and gained 9oz in 5 days! But last night she slept almost through the night which is not like her. I had to finally wake her up after 4-5 hours to feed and then she only fed for a short period and went back to sleep right away for another few hours before I woke her up again to feed and again - only for a short period. My breasts were so engorged. The last few days since we brought her home she takes a few tries to get her to sleep in the bassinet and usually only sleeps for 2-3 hours at a time at her best. Has anyone else experienced a newborn sleeping well this early on? I did call the doctor's office and they said not to worry and to monitor for now.