I think it's different with every baby. My little girl is 5 weeks as well, and she drinking between 60-90ml feeds every 2-3 hours, for the most part. One time at night, she will sometimes sleep between 3.5-4 hours so I let her sleep rather than waking her. I don't worry about it too much either way because she wakens to feed on her own and she is gaining normally.
A poster at my doc's office stated that a newborn to 6 months (I believe) ought to eat 60-100mls per feed. We just had her weighed yesterday and she is doing great. If she doesn't want to eat, she won't, and frankly, I do not force her to save a bottle--they are pretty much tossed about an hour after beginning the feed, regardless of the amount she has consumed.