Baby boy wasn’t getting enough nutrients from breast milk

My little man is 5 weeks old today. I just recently switched him to formula because he wasn’t gaining weight properly just from breast milk. At first he just didn’t latch well. And if he did, he’d only nurse for 5-10 mins, so I bought a nipple shield. That helped his latch a lot, and he’d nurse for about 15-20 mins then. I even tried pumping, I’d get about 4-5oz from both breasts combined. But he still never seemed satisfied, so I switched him to formula about a week ago and he’d already gained a half a pound. He drinks anywhere from 2-4 oz and I’m pretty sure he’s cluster feeding right now because he’ll drink 3 oz like he’s starved and an hour later drink another 2-3 oz. I can already tell a difference in his weight, just from holding him. He looks and feels chunkier and it’s making me so happy. I’m really bummed my breast milk wasn’t good enough for him, but I’m so glad he’s doing so good on formula now! ❤️