@lykos, what LucH said. Along with fatigue and poor copper metabolism, having low iron despite adequate intake is another sign of an under-active thyroid. Despite my intake of iron-rich foods like red meat and supplementing with food-based iron, my ferritin was down to 6 and didn’t budge until I started taking thyroid (Armour). I was also diagnosed with mold toxicity and gut dysbiosis (SIBO), which cleared up when I targeted my thyroid. To rule out your symptoms being thyroid related, if you haven’t done so already, you may find it useful to track your temps (including extremities) first thing in the morning, and before and 20–30 minutes after you eat, and also your pulse rate, for two weeks. And in case you haven’t read it, here is Ray Peat’s article on TSH, temperature, pulse rate, and other indicators in hypothyroidism:
https://raypeat.com/articles/articles/hypothyroidism.shtml