Cramps can come from hypothyroidism or hyperthyroidism ~ and of course, the classic lack of potassium. Best thing to do is keep track of your thyroid hormone levels, and after that make sure you are hydrated and have adequate potassium. When your thyroid hormone levels are out-of-whack, you can still minimize the cramping with hydration and adequate potassium. As levels normalize and stabilize, the cramping should go away.