baby previously sleeping through night now wakes up every 2 hours

my baby is breastfed and supplements about 1-2 bottles at night of formula. he usually sleeps about 8 hours in the night. but as of lately he has been waking up every 2 hours. he also wakes up right away when I put him down for his naps throughout the day. I should also mention he is 2 1/2 months old. he used to sleep well, about 1-2 hour naps during the day regardless of putting him down. why would he change his habits?? 😔