Formula and Sleep

Hey guys! My LO is 3 weeks old and we are formula fed. My doctor switched us to Enfamil NeuroPro 2 weeks ago due to constipation issues on Similac Pro advance. How ever, I have noticed since the switch that my LO is waking up every 2.5-3 hours to eat and he does he is Hungry!! We are doing the recommended 32 oz a day.. I’m just concerned that he is eating so often. I thought formula fed babies are supposed to be fuller longer and eat ever 3-4 hours. Any thoughts ? Is it the formula and it being close to breast milk? Is it a growth spurt?