Formula

Has anyone's baby became constipated on powdered formula? My daughter is 5 weeks and was on the ready to eat enfamil gentlease up until last Thursday when I began the same formula, just powdered. And now her poopie is starting to get firm and comes out in pieces. She's still eating fine and isn't straining, but I'm worried it will get worse if I don't go back to the ready to eat formula.