This is not medical advice: I have no qualifications nor registrations. Hypothyroidism is full of some really fucking harmful quackery on the Internet. Please avoid those bad websites. You're right that it needs careful monitoring to get the dose right. A general supplement of vitamins A,C, and D is probably not harmful. (Do not overdose on vitamins. They can be toxic and can kill.) And now some other stuff: Work tow…
"the internet" helped me there loads more than any medic, this became painfully clear when I started to bother to read official documents that medics should have been reading, for example I saw on internet a study that was about specifically my case, all doctors I went refused to trust the study and said they only trusted the association and the lab numbers... I asked the lab their source, they pointed me a association-made document, I read the document, and behold, the official association document that the lab and doctors claim to follow, cite the study I was citing, and for precisely the same reasons...
I could only conclude that doctors are lazy, and like to take whatever number someone (their teacher, lab, whatever) spoon fed them, instead of reading the source of that number (including the endocrine association guidelines... seriously, I went to 8 or 9 different doctors in the last 12 years, some of them absurdly expensive, and not a single one read the guidelines, despite all of them claiming to follow them!)
What is CBT and IAPT? Google keep throwing me stuff on my own language, despite me using english as default (for example for Google CBT is the brazillian tennis confederation).