Welcome to the forum and congratulations on the new baby! I am so sorry to hear that he came so early. I hope he's able to go home as expected!
On to milk production. Milk is produced on a supply = demand basis. Demand more milk from your body, and you will produce more. The best way to do this is to pump more and to use the right pump. For most moms in your situation, that means using a hospital-grade pump with correctly sized shields, and using it about 8-10 times a day, or more often if possible. 6-8 pump sessions is a lot of work, believe me when I say that I know! But it's not enough for most women to maintain a good supply.
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"