Breast milk not filling enough?

Our baby is 5 weeks. He wasn’t gaining enough weight when I was EBF the first few weeks, so we supplemented with formula. He can easily go from breast to expressed milk in bottle to formula in bottle. What I am noticing is, he seems to not be satisfied with breast feeding directly. He’s also fussy at the breast, so I usually end up transitioning to bottle. If I give him 3-4oz of expressed milk in a bottle, he’ll still be hungry and I will give him 2oz of formula. If I do a feeding with only formula, he’s usually satisfied after 3.5oz. Because of this, it’s almost easier to just formula feed, but I know the benefits of breast milk. It’s just all a lot to pump and/or mix formula, or to do more than one thing for a single feeding. I’m not sure what I am even asking or complaining about. Just want to know that I am not the only one. (cry!) And don’t know how I am going to go another 5-11 months with breastfeeding/pumping.