feeding help!?

My daughter is 3 weeks and 5 days old. For the past about 4 days she will nurse for about 10 minutes, unlatch and cry. I keep offering about 3 times and she won't have it so I give her her pacifier and she takes that and falls asleep, wakes up about 2 hours later to eat again for about 10 minutes to do the same, unlatch and cry and not nurse again even though I offer. Before this she was eating about 30 minutes and very happy. She has had a lot of dirty diapers so I believe she is getting enough milk but why would she go from eating 30 minutes every 3-4 hours to now 10 minutes (and not acting very happy, arms swinging, legs kicking) every 2 hours.