Pumping Milk (HELP)

Ladies so I am an first time mother. I only breast feed my baby since he was born. Well the first days at the hospital I gave him formula they provided since my milk wasn’t coming in yet. But after that it’s been only breast milk. I am about to start work again and I want to pump milk for my baby to continue breast milk but when I pump not much comes out sometimes only less then 1oz and other times 3oz and I believe only once I pumped 5oz. So does anybody have any helpful tips on how to get more milk to pump?

My baby is 2months and eats constantly.