Pumping

My daughter is 7 weeks, I returned to work with a small stash because I was steadily breastfeeding full time while on leave... since I've returned to work I notice I only get about 12-13oz per 8 hr shift....

When home I am breastfeeding I honestly think this is low in oz for an 8 hour shift... am I crazy? My daughter eats 3-4oz per feeding