Pumping

I have the Spectra Electric pump (the blue one). I am exclusively breastfeeding, and trying to build a supply so I can store milk for going back to work. I don’t pump often, because i typically attach the Haakaa - but at least once a day I’ll pump one side while I nurse. With the Haakaa I’ll catch at least an ounce. When I attach the electric pump for 20 mins I’ll get maybe an ounce, if that. Is this normal? My baby is almost 6 weeks old. I know I’m not going to pump four ounces from one side, but why am I getting more with just the Haakaa? Any pumping suggestions?