Low milk supply! How can I increase my breast milk?

Hello Mommies !! I had my daughter at 27 weeks and she is staying in the nicu. Been there for a month and is now 31 weeks. I been pumping maybe 5x a day when I wake up . But 2x I went with out pumping for 6 hrs. And today I haven't pumped not 1 oz . It's frustrating me because my baby really needs this. Does anyone have any pointers to increase my milk supply fast !?