pumping

Maureen
I've been EBF for the past 4 weeks and I'm wanting to start building a supply for when I go back to work. My question is Do I need to pump after each feeding or just a couple times a day? So far I've just been pumping after baby eats first thing in the morning and I usually get 3oz total from both breasts and he has eaten off both breasts before I pump! Any advice or thoughts welcome!