Clumps of formula??

Ap

Hi! I’ve noticed a few times lately that when I mix a bottle of formula there are clumps in it! I have to make a new bottle and it’s so wasteful...that formula is expensive!! We use Dr. Brown’s bottles and Enfamil Gentlease formula. I’m a first time mom. He’s four weeks old today. What’s the deal with the formula? What can I do besides stirring every bottle with a fork?