Low supply with pumping

My baby is a week and a half 2 days ago I pumped 41oz now all of a sudden I only get 10oz in 24 hours and I’m worried my milk is already drying up. I need to keep pumping a lot so my bf can feed her at night when I’m too tierd and I don’t want to be the only one that can feed her. I’m extremely worried. Is this normal? how can I keep my supply up more so I can keep a large freezer stock for other people to feed her.