I just pumped 13oz. Not over the course of a day, but in one sitting. And I don't EP; I exclusively nurse except for about a 4 hour stretch on Monday nights.
This is not normal. This is called oversupply. Many moms seem to think that this is a wonderful thing, but it can be a problem. It is often accompanied by overactive letdown, which causes milk to go shooting out of your breast (picture the difference between sipping from a straw and trying to drink from a garden hose that has been turned on). Babies whose mothers have oversupply are often fussy, they pull off the breast, have colicky cries, are gassy, and spit up a lot. They may gain a lot of weight really quickly or they may not gain enough weight. They may also have green and watery stools resulting in red, sore bottoms. Mothers with oversupply are more prone to engorgement, plugged ducts, and mastitis. Sometimes, they have painful letdowns because the force of the milk coming down is so strong. If you are suffering from complications related to oversupply, here are some tips to help get it under control.
The normal pumping output is 1/2 to 2oz from both breasts in one sitting. Babies are more effective at getting milk from our breasts and what we pump is not an indication of what we are making. Plus, our bodies know the difference between being cuddled up to an actively nursing baby and being hooked up to a machine and we often don't respond as well to the machine.
If you're not pumping enough to feed your baby while you're away, you should first determine if the caregiver is overfeeding your baby. When baby is overfed while away from baby, it is very difficult for mom to keep up. You should be leaving a max of 1.25oz per hour that you're away from baby. If they're drinking more than that, then they are being overfed.
If you have determined that you're baby is not being overfed, there are many tips to get more milk. Try to throw in an extra pumping session or two while you're at home with baby. Pumping while nursing works with your baby triggering the letdown and often results in more milk than using the pump alone. Looking at a picture of your little one and/or having a baby blanket or article of clothing that you can smell can help; effective letdown is very sensory. Visualization is often very effective for helping with letdown, so try to visualize your breast filling up with milk. You can also try things to increase your supply, such as eating oatmeal, taking fenugreek or other galactagogues.
Do not expect to pump massive quantities of milk. We are, after all, humans whose babies only need a little bit of milk at a time.