A newborn or any age baby including a 3 month old baby pooping after every feeding is normal.
When a breastfed baby poops after every feeding it's a good sign that the baby is getting enough milk so you're certainly feeding the baby correctly and enough to keep them healthy.
Babies who are formula fed sometimes poop less often and don't always poop after every feeding but it's still normal for a 3 month old baby who's formula fed to poop after every feeding as well.
Unless the baby is having excessive diarrhea then there's nothing to worry about if your baby is constantly pooping every time you get done feeding the baby.
It's very normal in some babies but all babies are different and some may poop after every feeding while others may not.