If you have already been breastfeeding, you can begin pumping around four to five weeks. By then, breastfeeding is well-established. Also, you don’t need a stockpile. Just start pumping a couple weeks before you go back to work. Make sure to pump after feeding so you don’t interrupt the next feeding.
Make sure to pump any time your baby is getting a bottle. Your body learns how much milk to make based on what is removed. So, if your baby is getting a bottle, you are still making the milk and it needs to be removed. When bottles are given without mom pumping, it can decrease your supply.