How much milk should I be able to pump in one session?

teachermother

I am starting to pump at least 1x a day before I go to bed (for comfort more than anything)  I never get much, I sometimes barely get 2-3 oz... is this normal?  I am obviously making enough milk for my LO as she is gaining weight as she is suppose to and is content between feedings every 3 hours.  I am concerned I will not be able to keep BF when I go back to work because that is not even enough for 1 feeding when she gets older and I teach so I will not be able to pump ALOT during the day just mainly in the AM before work at lunch and at night if Im lucky.  Any advice would be greatly appreciated!