How to up milk supply

I’m 2 weeks postpartum and pumping. I planned to exclusively pump as I have to go back to work in two more weeks but as of right now I’m supplementing with formula as well since my supply seems to be low. I pump every 2-3 hours. 15 minutes of pumping if it’s been 2 hours and 20 minutes if it’s been 3 hours. I only get about an ounce and a half- 2 ounces each session though. And that’s combining the milk from both breasts.

I make sure to drink a gallon of water every day, I pump regularly, I’m still taking prenatals and make sure to eat well. How else can I increase my supply?