poop problem

mga momsh please help. 4days na hndi nag poop yung baby q from the time na ng change aq ng milk from ebreastmilk to formula (similac) mixed feed. after 3days na hndi sya naka poop ay hndi q na sya pina take ng formula milk pina exclsive q na sya sa breastfeed. pero wala paring poop. 4days na. 1month plang po sya. normal po ba eto? After dede nya skn fuzzy sya then farting tas kalmado na sya. Thank u mga momsh