The POTS wouldn't cause anemia but anemia could make the POTS worse by further decreasing the supply of oxygen to the brain when you stand up. Also, iron deficiency could make heart muscle and blood vessel muscle tissue work less well.
I have trouble believing you had the iron deficiency without anemia.
If your iron isn't low, you shouldn't be taking iron. What kind of diet were you following? No meat vegetarian is the most common though as many Indian vegetarians prove, you can get iron from vegetable sources like leafy greens.
Do other people in your family have POTS? Do you have Ehlers-Danlos (double jointed, can pull skin out far)? Do you have problems with chronic fatigue or with restless legs?