New to pumping

Morgan
My son is a month old and I'm a FTM. I've decided to try to start pumping to make a stock pile for when I go to work. Last night I did it and got 2 ounces. Tonight I did it and I barley got anything. I usually do it after feeding my son. Am I doing something wrong? Do I need to do it every other day to start out with? I'm only pumping once a day