Hi,
I've been working hard for months to figure out why I had such severe and prolongued side effects from my AZ vaccine, and I'm coming to realise now that it is probably because I am quite deficient in some vitamins and minerals, mostly iodine and vitamin B12. (Both of these show in NHS blood tests - as low T4 and low-normal B12).
I wondered if I could mention in case it helps anyone else who is struggling to return for their second vaccination?
In my case, the reason for the deficiency is a gut problem that causes intolerance to a lot of foods, and also to all vitamin supplements, so it's a bit tricky to fix, but at least knowing what the problem is, is a start.
I'm following the instructions on this website below, to try to resolve the problem. It uses vitamin solutions that are spread on the skin, rather than swallowed, so is meant to be kinder for people who react badly to vitamin pills.
b12oils.com/rnb.htm
I tried iodine on my skin and dietary B12 from turkey so far and both made me feel radically better quite quickly.
Very big thanks to @CrunchyCarrot, for explaining this system to me. 



I hope that posting this here might help others in the same situation.