@donnaburch ,
Have you looked into a condition called Beriberi? Many POTS patients (like myself) are misdiagnosed with POTS where they really have a condition called Beriberi. All that is needed in that case is B1 (thiamine) supplements (or injections in my case).. This is especially common among those patients who also have some kind of IBS which does not allow their digestion track to absorb B1 from food.
I recommend googling the word POTS and Beriberi together.