When symptoms persist even when thyroid replacement results in «normal» lab values it can be due to thyroid hormone resistance (poor thyroid receptor function). (yourhormones.com)
Also, women have fewer thyroid receptors than men, making them more sensitive to small decreases in serum levels of thyroid hormones. (verywellhealth.com)
This is due to the fact that a predominance of thyroid receptor sites are found in the brain. (mindbodygreen.com)