how much does your 6 week old ff baby eat?

So we recently switched my LO's formula to similac pro-sensitive because we were dealing constipation and reflux. My 6 week old eats anywhere from 2.5-5 oz of formula every 2-3 hours. Hardly ever goes more than 3 hours, even at night! Is this normal? I hear all these moms saying their 6 week old only wakes up once through the night to eat and we are still waking up 3 or more times a night. I feel as though we can't get a routine down.. any thoughts? He's gaining weight fine, but I just feel like he should be taking more in or starting to go longer between feeds? Sorry, FTM and extremely anxious. Just wanna know that we're doing the right thing!