Increase milk supply

LJ • Baby girl born Feb 19, 2015 and second girl born Jan 20, 2017. Baby #3 due in October!
I am currently pumping throughout the day but am not able to produce enough milk to keep up with my baby. She will be three weeks in a couple of days and she's drinking between 2.5 to 4 oz each feeding. Some of those feedings are hourly. When I pump I normally get around 2.5 to 3 oz total about every three hours. Should I be pumping more often. We are still working on latching issues so she isn't breastfeeding often at all. Any products to try eating or drinking? I've heard of fenugreek and mothers milk tea but I haven't tried anything yet. I would just rather have my baby only drink breastmilk and not have to supplement with formula.