Re: Worried about my supply
If you really have low milk supply, this would probably be the best way to help it. (sorry!) It won't hurt your baby to be encouraged to nurse at night. You could consider some form of co-sleeping (sleeping in close proximity) & nursing in a side lying position so you do not need to get up. And/or you could nurse right before you go to sleep instead of pumping. A 10 hour stretch of sleep is about twice as long as you would normally expect at this age. (“Sleeping through the night” for a baby is defined as a 5 hour stretch.) Great you are pumping once during that time, that certainly helps from a milk supply standpoint, but I am sure you are aware that nursing is more effective than pumping in maintaining milk supply, plus if you nursed that would be more milk for baby over that long stretch.
I really don't want to wake her or to get up in the middle of the night.
Yes. You could consider troubleshooting your pump to try to improve performance, but this is a normal per session pumping output.
When I pump at night or when I'm at work without her, I only get 2-3oz per session after pumping both breasts simultaneously for around 15-20 minutes. Is this normal?
Here is the thing-you may have fine milk supply. I can't tell from what you have posted, pump output tells us nothing about supply, and lots of moms think they have low supply at around this age and they are fine. Also, lots of babies are inadvertently overfed with bottles by their caregivers and that is why they run out of milk (see paced bottle feeding link & milk calculator link below) BUT…
When there are low supply issues arising at this age, it is often caused by 1) long sleep stretches at night and/or 2) regular separations. Even when mom is pumping regularly at work, it does not have the same effect as a baby nursing regularly for the average mom. Some moms have tremendous supply and these things do not affect them so much, but others with normal supply may struggle with low milk supply issues when they go back to work and/or baby starts having a long sleep stretch.
What to expect when pumping: http://kellymom.com/bf/pumpingmoms/p...-when-pumping/
How much expressed milk does baby need? http://kellymom.com/bf/pumpingmoms/pumping/milkcalc/
Bottle feeding the breastfed baby (prevents overfeeding as well as helping with other issues: http://www.llli.org/docs/00000000000...astfedbaby.pdf
Low milk supply: http://kellymom.com/bf/got-milk/supp...es/low-supply/