Make sure you are eating and drinking enough, that is key. Also, make sure you are relaxing when you are nursing and pumping. Generally, a women gets more milk out when actually nursing as opposed to pumping, so she may be getting more from you when she is nursing.
There is a natural tea sold at health food stores, it's called mothers milk I believe, I have heard that it works wonders.
From my understanding, the only way to increase breastmilk is to feed or pump more often. That will increase your milk supply. The more you breastfeed, the more milk you will produce. Make sure you stay hydrated with plenty of water and liquids and get enough calcium.
I do think there's a pill the doctor can give you if you're really having a hard time producing but I'm not sure how that works. I'd ask your ob doctor.
Best wishes!