When to pump...

Michelle
Exclusively breastfeeding and trying to build up a stash of milk. ...not sure when is the best time to pump? Like 10 minutes after nursing? An hour? Just worried that baby will want to feed right after I pump. I've pumped a few times and the results are laughable. I had to pump last week as my baby was in hospital and unable to nurse and I was getting 30-40 ml easy from each breast...now it's like 10 ml maybe. Any advice would be appreciated!