Carthage may come up with some better reasons as to why you might test normal with low thyroid symptoms.
I have been battling this as well, have been on thyroid meds for close to 2 years but still have symptoms. Am also on low dose cortisone for adrenal fatigue for 16 months and although better they are still not healing by current test results.
Cortisol is necessary for your thyroid hormone to do its job and get to the receptor sites to alleviate symptoms. When your cortisol is low the thyroid hormone just sort of pools in the blood and you will test normal or even a little high all the while having a lot of symptoms.