Increasing Milk Supply

Is there anything that actually works to increase the amount of breastmilk? I am only able to pump barely 2 ounces total for my baby. Now it is enough to feed her, but not enough to have a supply. I pump every 3 hours on the dot and I drink tons of water, but nothing works. I don't need a giant supply, but just enough that my baby doesn't have to wait until I am done pumping to eat. Also, I am working on being able to breastfeed her, but she was 3 weeks early so it is still a work in process. That is why she is having to wait until after I pump to eat.