Need Pumping Help

Sarah
I'm exclusively breastfeeding, not substituting any formula nor do I plan to. I'm producing more than enough milk for my baby girl, she's almost 4 weeks old (and has gone from 6 lbs to 9 lbs in 3 weeks). My milk spills from one breast while she eats from the other, yet I get almost nothing when I pump. I can see it build up around her mouth and hear her swallow and sometimes it even comes out too fast and she gets a little choked. The only thing that has helped is to have her eat from one breast while I pump from the other and it's not that much (3 oz tops from both breasts combined). Do any pumpers have any advice they can offer? I need to stock up for when I return to work. Thanks in advance!