Pumping frustration

I'm 3 weeks PP and am exclusively pumping. The max I've ever gotten in one pump is 5.5 ounces but mostly I get between 2-4. Is this normal? I basically pump just enough for most of her feedings and am on this constant hamster wheel. I feel like I'm never going to pump enough to not have to supplement or build up reserves when I go back to work. I don't want to give up but I feel so discouraged. I'm taking every supplement and guzzling water all day but only see minimal improvement. Anyone else struggling with this?