[Breastfeeding Myth #3]. There is no (not enough) milk during the first 3 or 4 days after birth.
It often seems like that because the baby is not latched on properly and therefore is unable to get the milk that is available. When there is not a lot of milk (as there is not, normally, in the first few days), the baby must be well latched on in order to get the milk. This accounts for "but he's been on the breast for 2 hours and is still hungry when I take him off". By not latching on well, the baby is unable to get the mother's first milk, called colostrum. Anyone who suggests you pump your milk to know how much colostrum there is, does not understand breastfeeding, and should be politely ignored. Once the mother's milk is abundant, a baby can latch on poorly and still may get plenty of milk.
from Some Breastfeeding Myths http://www.kellymom.com/newman/11some_bf_myths.html#3