pumping help!

My LO is 2 1/2 weeks and I am having to exclusively pump. I produce between 2-3 ounces each time I pump, but she is eating 3-5 ounces each feed so I have to supplement with formula. I want my supply to increase, and I pump every 2-3 hours. How can I get my supply to increase fast? I'm afraid I won't produce any more, especially when she eats more. Do I need to pump every 2-3 hours at night too? Please help, I hate supplementing with formula