Hi mama! Alamak, don't worry lah, selang sehari or even 2 hari sekali is completely normal for FM babies. Formula fed babies tend to poop less frequently compared to breastfed ones, and as long as the poop is soft and baby looks comfortable (not straining or bloated), you're fine. Some babies settle into a routine of once a day or once every 2-3 days, and that's their normal je.
The main thing to watch is the consistency, as long as it's not hard or pellet-like, and baby is gaining weight and seems happy, the doctor won't worry. Dupro is good milk, so I wouldn't stress about the brand. Boleh la check with your pediatrician just to be sure everything is okay, but honestly this is very common with FM babies especially once they pass the newborn stage!