Best formula

Hello ladies my baby boy is 3 weeks old. I'm breastfeeding, but lately it seems like he isn't satisfied and I'm supplementing with Formula Enfamil newborn. Ive given him some in the past once a night. Last night I did two feedings of formula. It seems like he spits up a lot maybe I'm doing something wrong? I'm feeding him 2.5-3oz which is the same amount I've used previously and and he's never had a problem till last night. Can it be because I did two back to back formula feedings? Is there another formula that you can recommend?