D.,
Amy N gave you good advice. What she's suggesting is called "power pumping" and it works.
Frequency of pumping is probably one of the most important things. Since the pump stimulates you differently (usually less) than your baby, you need to pump at LEAST every 4 hours - if not 3.
Also - this is going to sound funny but every time I ate the Indian dish "Dal" while pumping (and I was a low supplier the whole time), my supply JUMPED! I think it might be the fiber or some kind of hormone inhibitor because Metamucil would do the same thing.
Beer, fennel, fenugreek, oatmeal, carrots and more are lactogen inducers.
You can get more info on increasing supply at the following websites.
http://www.mobimotherhood.org/MM/default.aspx
http://www.kellymom.com/
Great job on continuing to provide your baby with your best while working outside the home. It's a big job. Remember that the overall experience of mothering is more than milk production though, ok? You need to get rest and maintain as much balance as possible while working and having a small child.
Blessings.