Pumping while breastfeeding, HELPP🤱🏻🙏🏼

I really want to pump but I don’t know when to do it. My son is 2 months old, he eats every 20-45 min so I don’t really know when to pump, he naps but like for 10 min-15 min and then he wakes up. if I pump and then he wants to eat he will get pissed because my breast will be “empty”. Help! I’m only pumping at night but I only get 1-2 oz to 4-5 max.