Left full Right...not so much

My left breast will pump 2.5 oz a session. My right one only pumps between 1-1.5/session. Should I start pumping my right one more frequently? I switch breasts every other feeding but sometimes he eats for less time in one feeding then the other. Should I feed on that same breast again he next feeding? Should I only pump for a certain amount of time rather then to a certain oz level? I'm a SAHM so I only pump to make enough for when I'm at the grocery store/a doctors appointment or for in the middle of the night if I'm too tired to breastfeed. We also have been giving him formula a few times a week so his stomach is used to it in case of emergencies. The other night for some reason I was pumping and hand expressing and NOTHING was coming out but a few drops. He'd cry while nursing because he wasn't getting anything. Totally weird. So we had to do formula. Anyway. I was pumping a lot while first feeding due to nipple scabs and I was always engorged. I was pumping 2.5 oz per side after about 10 minutes. I started hand expressing which helped tremendously and I wasn't engorged anymore. But now that I've started pumping once a day my left breast gets engorged. Occasionally my right will too but there is way more in my left. I'm trying to have this make sense lol. How can I best even it out while still being able to pump once or twice a day for a small stash for when I'm gone for a few hours and not be engorged? Thanks