Not eating enough?

Kate
My 6 week old has never nursed for long but recently it's gone from an average of 12 minutes/feed to only 8. She nurses 8-10 times a day and it's gone from about 2 hours total feed time to only a little over 1 hour.  I try to offer more but she pushes off and falls asleep.
Is this normal?? If not, is there anything I can do to get her to eat more?