My daughter cluster fed at that age too. Lasted 1-2 weeks. Sometimes I didn’t have enough supply, so we’d top up with formula. Keep your wife hydrated, help her top up with formula when she’s tired. For the record, my LO still sometimes latches for 2-3 hrs. It’s very tiring
It's likely a growth spurt period, so like you said baby will cluster feed a lot and more needy and cranky. Mine lasted about 2 weeks. If your wife is tired she can try side feeding by lying down and having baby on her side. I bf only in that position now, very relaxing :)
3 weeks old seems too fast to cluster feed. You can try reading up on mental leaps.