Infant feeding HELP

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My son is 6 weeks old. When he was going through his growth spurt he went up to 4 oz and some times wanted more. Now i feed him his 4 oz and then he spits up what seems like every bit of it. I.meam soaming the whole front of.his shirt, my shirt. Several clothes changes. He seems uncomfortable. Should i take him back down to 3? From 4 to 7 am hes pretty upset crunching and bending.