TSH is a pituitary
hormone and is not a good indicator of thyroid
hormone levels. Many of us on thyroid replacement have TSH levels that are low or suppressed. My own TSH lives at < 0.01; hasn't come up in 5 years, no matter how much my med is lowered, yet my FT3/FT4 are sometimes lower than they need to be to alleviate symptoms.
TSH neither causes, nor alleviates symptoms, and once on medication, it often becomes totally irrelevant.