Help! Breastfeeding a baby that was a Preemie

My baby is 8 weeks old and he was born at 34weeks. I started breastfeeding him a week after he was in the nicu, and now that he’s home I put him on the breast for about 20mins and then supplement with formula because I have to (doctors order) and I don’t produce enough to satisfy him.

I have tried every food/drink/supplement/ & pumping/hand expressing. I don’t have a pump anymore but I would love some tips or advice on how to establish a good supply. I try using a Haaka on the other breast but I don’t leak anything.. HELP