Good advice from above :) Also, I thought that a newborn should be getting roughly 2-3 oz. of milk/formula per feeding for the first month. So, if you are pumping 2-3 oz. that is good! If you are pumping more... store it up for later use... or at least that is what I am doing :)
A woman's milk supply is based on the demand of the baby. Normally you little one would be nursing at night so your body would make enough to cover that time. Because you aren't pumping at night your body does not 'think' your baby needs more than it is making. In order to increase your supply try pumping more often and leave the pump on for a minute or two after your breast is emptied. This will tell your body that it needs to produce more milk. I hope this helps! Good luck