M.B.
A.,
Pump more often. Drink water a little more often. Are you close to your period? Put your daughter to the breast, even if you feel empty.
Try pumping 10 min at a time, and spacing out the times instead of trying to get it all at once. (or 20 min or whatever. I don't know how long it took you to get 5-8 oz).
http://breastfeedingonline.com/newman.shtml
The more you remove, the more you make.
There's a lot more out there! Just relax and take it one step at a time. Stress does not help.
Good Luck!
M.