Pumping

Adds
I'm pumping to try to build supply up for when I need to leave the baby with my husband for 7/8hours in 2 weeks. 
I breastfed my son only on one breast and my non-empty breast only yielded a little more than an ounce (the breast I fed on was like barely anything).
I've been struggling breastfeeding with my son- feeding him non stop and now I'm thinking it might be low supply? What's a Normal amount to pump (I'm 3wks pp)