Inconsistent expression

The problem I am having is that I can express 7oz followed by 5oz in the morning but by the afternoon it’s down to 2oz and then by bedtime I can only get about 1oz. This is challenging because my daughter (4 months) likes to eat big at night and I feel like I am constantly pumping and nursing at night to feed her.

Typical pumping sessions:

5:30am - 7oz

9:00am - 5oz

12:00pm - 4oz

2:00pm - 3oz

4:00pm - 2oz

5:30-9:30 Desperately trying to feed the baby. Maybe 1oz an hour.

Does anyone have this same problem and/or have any advice how to fix it?