Head lean

Hey IM's
Yesterday i noticed my 4 month old's head is leaning towards one side. Its has never been like this before. He doesnt seem to be in any discomfort but it has .e concerned nonetheless. I read it could be torticollis but that's generally something they have from birth and its related to their favored side to lean on. This would make sense however his favored side is the opposite side as its slightly flat and ive been trying to rotate him for a while now.