Thyroid keeps shrinking and getting larger?

The thyroid doctor said I had to have the whole thing removed and pills wouldn't help. If this is true, then why does my thyroid shrink smaller when I eat different foods with iodine in them like meat and get larger when I don't? Do I really need surgery if my thyroid repeats a pattern of getting bigger and smaller? Is is just iodine deficiency or is it an inherited hypothyroidism or hyperthyroidism?