Most moms who are nursing full-time are able to pump around 1/2 to 2 ounces total (for both breasts) per pumping session. Moms who pump more milk per session may have an oversupply of milk, or may respond better than average to the pump, or may have been able to increase pump output with practice. Many moms think that they should be able to pump 4-8 ounces per pumping session, but even 4 ounces is an unusually large pumping output.
It is quite normal to need to pump 2-3 times to get enough milk for one feeding for baby (remember that the pump cannot get as much milk as a baby who nurses effectively).
Many moms are able to pump more milk per session when they are separated from baby. Milk pumped when you are nursing full-time is "extra" milk -- over and beyond what baby needs. Don't get discouraged if you are trying to build up a freezer stash when nursing full time and don't get much milk per pumping session -- this is perfectly normal and expected.