You should ask your GP to do thyroid function, vitamin D and ferritin tests as low levels of any of them can cause aching joints and fatigue. I don't know the symptoms of PA other than B12 deficiency but you can get advice on healthunlocked.com/pasoc
There is no cure for autoimmune thyroiditis (Hashimoto's) which causes 90% of hypothyroidism. Treatment is for the low thyroid levels it causes. Many people have found that 100% gluten-free diet is helpful in reducing Hashi flares, symptoms and eventually antibodies.
Recommendation for D3 Solgar 2200 IU, I take one a day and I live in a sunny climate. You can buy them in any good health store but be aware that you get a strong enough dose, I know another friend who takes twice this amount a day and I believe what the NHS prescribes is not good enough.
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