Before changing your baby’s feeding routine, you should first consult with your doctor. Any changes may result in temporary digestive issues, like gas and spitting up1, that can in turn cause fussiness.   Here are recommendations related to switching formulas: • Don’t alternate or combine the new formula with the formula you’ve been using • Transition directly to the new formula. • Don’t mix different formulas. • Allow your baby 3 to 5 days to get used to the new formula.   For a more detailed look, read Baby formula: Switching formulas. 1Consult a physician if your baby is spitting up forcefully or frequently at every feeding and is not gaining weight.