It's well worth trialing pyridoxal-5-phosphate which is the body ready form of B6 if you haven't already, it certainly wouldn't hurt. 10 - 12% of the population are unable to covert B6 from supplements and consequently cannot use zinc properly which is needed for T4/T3 conversion. This was actually my problem and it took me 60 years to find out. If you cannot break down B6 you also cannot utilize magnesium properly either. There is a cheap urine test for this which picks up excessive levels of B6 and zinc, but I think it is best to go by symptoms. As I said above, you are not converting properly which means the body is lacking something. Pyroluria is a common metabolic condition in which pyrrole, a key component of haem as in haemoglobin, is overproduced in the liver and bone marrow. The surplus binds to vitamin B6 and zinc and is excreted in the faeces and urine, but part of it tends to remain in the body as obstructive waste residues. This creates severe deficiencies in B6 and zinc, and to a lesser degree in some other nutrients, such as niacinamide, gamma linolenic acid (GLA), biotin, and sometimes manganese; also other B-vitamins, especially vitamins B2, B3 and B5, may be low.
Vitamin B6 and zinc are essential for producing enzymes that are required for building all proteins, be they other enzymes, hormones, and neurotransmitters, components of the immune system, muscles, organs or connective tissue. Another major problem is that pyrrole waste chemicals tend to inhibit the conversion of pyridoxine, the common form of vitamin B6 in food, into its active form pyridoxal-5-phosphate or P5P. In a vicious circle deficiency of P5P reduces the synthesis of haem and haemoglobin, and increases formation of pyrrole wastes.