iodine and selenium need to go hand in hand, I would up your selenium dose to 400mcg a day and see if that help and if not after a couple more weeks up it to 600mcg.
Selenium also recharges glutathione so if your low in antioxidants a good portion of your selenium may be going to glutathione and not the thyroid. With that in mind you may want to consider greatly increasing ascorbic acid intake to as much as you can handle daily without diarrhea.