Animas

If it’s part of a series it sounds a bit like “Otherkin” by Nina Berry, or “The Land of Elyon” series by Patrick Carman, or even “The Firekeeper's Daughter" (specifically, the first book, "White Tiger") by T.K. Stewart. But I think these all have shapeshifting elements in them, too. It’s highly possible you read an ARC of book 3 (which was cancelled) of the Animas series which follows a boy named Bailey Walker who communicates with a worm.