I had the same concern for a while, but I've found that even if Billy wakes up and is hungry shortly after I've pumped (he's woken up as little as 10 min after I've finished pumping), he seems to manage to get more out of me! Usually I feel another letdown after a min or so of him starting to nurse. I never thought that would happen, but the whole "on demand" thing seems to be true! Apparently your body is smart enough to realize that more milk is needed. Also, from what I've found, the babies are MUCH more skilled at getting milk from you and can get more than the pumps!
My suggestion to you is one that was given to me... pump after every feeding if you can do it... That will help to tell your body that you need to produce more milk and will help to build up your supply.
Good luck with your bfing and congratulations on your little girl!
__________________
Me 36 (now 37) fibroids mild endo
DH 40 (now 41) no issues
Dx unexplained infertility
TTC 16+ mths
'08
6/27 Start BCP
7/15 BIG BOX OF MEDS
7/17 Stop BCP 10U Lupron
7/21 
7/23 Stims 2 Bravelle+2 Menopur
7/24 Lupron 5U
7/26 E2=426 1 Bravelle+2 Menopur; 7/28 E2=1034 2 Menopur ; 7/29 E2=1764 2 Menopur ; 7/30 E2=2882 1 Menopur ; 7/31 E2=3900 1/2 Menopur ; 8/1 E2=4240 TRIGGER 9:20pm ; 8/3 ER 9:20am 12 eggs ; 8/4 8 fert ; 8/8 ET 10:50am 
2 blasts ; 8/10 1 snowbaby
8/18 Beta1=159! I'm 
! ; 8/20 Beta2=397 ; 8/22 Beta3=771
9/2 US 1 little guy 2.5mm hr 120
9/9 US 10mm hr 143
9/15 OB release
10/16 NT scan perfect! ; 11/20 Rx fibroid pain ; 11/24 Rx=placenta previa ; 12/11 level2 US
IT'S A BOY!
1/15 US 2lb1oz ; 2/10 Rhogam shot ; 2/16 US 3lb11oz ;
3/19 US 6lb1oz!
4/16/09 William was born via emergency c-section! (7 lbs 15 oz, 21")
