Sleep vs. milk

My baby is now a month and 2 weeks old. Before, she used to drink about 5-6 bottles of milk (120 ml each) plus my breastmilk. But now, she sleeps a lot and only drinks about 4-5 bottles of milk (120 ml each but most of the time only drinks half a bottle). Because of this, a day can pass where she will not poo at all. Is this something I should be worried about? Or is this normal for babies this old?