Breastfeeding Supply

I am exclusively pumping with formula supplementation. When I pump, sometimes I will get 2oz from one breast, 1oz from the other. Then I will pump two hours later and hardly get any. pump two hours later and get a bit more but nothing to brag about. I am 4weeks post partum and just wondering, when will I start getting more! I try to drink water all day and that does help but I’m only able to give my baby a few bottles of breastmilk a day, 3oz at a time. Also have eaten oats, brewers yeast, and flax seed.