I have had this problem for a long time,although getting much better now. I always thought its from maybe possibly from high reverse t3 blocking conversion of t3 to the cells. Maybe the down regulation of the thyroid from the adrenals. Or maybe just from low cortisol?
Anyways, I have found that a few drops of licorice extract
helps....also small doses of zinc helps with the conversion of t4 to t3. Byron Richards make mention that zinc is a cofactor mineral that needs to be adequate for thyroid hormone to perform at an optimal pace. A lack of zinc is known to reduce the activity of TRH( thyroid releasing hormone in the hypothalamus).
Inturn tending to depress thyroid hormone levels. Zinc participates in the conversion of t4 to t3,and zinc is needed to bind active thyroid hormone to the DNA of cells. Zinc is needed for immunity,sex drive,and maintaining leptin status while on a diet. Its lost in sweat or STRESS.