I need help

Oh Moses this breastfeeding business is stressing me out!! My little man is a big guy, he’s 5 weeks and 12lbs, he was 9lbs at birth. I’m trying to figure out how much expressed milk to give him when I leave him for an afternoon. I know the standard is 4oz but we’ve started with that and a paced feed and he is inconsolable after until we give him more. Today I gave him 7oz before he settled and went to sleep. Is there a better way to figure out how much they need besides a feeding and then a single ounce at a time until satisfaction? My lactation lady said to give formula - not helpful. And my doctor just said to feed him until he’s happy - also not really helpful. I have a few more weeks until I go back to work but I know that’s going to be stressful too and the last thing I want to do is throw in the towel because otherwise nursing is going really really well!! (Also when I feed him a bottle pump to keep my supply and I get about 5oz from each side in about 20 minutes if that means anything)