i know exactly what the problem is - vitamin D and possibly A toxicity.
you are no doubt Iodine sufficient. a person in this state is able to maintain vit D and A in their receptors through normal diet. any kind of supplementing will cause an overdose condition. this hot spot is probably calcification of the soft tissue in the thyroid. stop the supplementation and take whatever steps are necessary for an overdose on those hormone-like vitamins and your problem will go away.