You seem to have been very thorough, but I would recommend getting your thyroid checked out. It’s not uncommon for your immune system to mess with your endocrine system too! In the mean time, maybe support your immunity with some basics like vitamin A, C, D, Aand E. Look into turmeric as an anti inflammatory. I do these to support my overall immune system health without ramping it into overdrive (some supplements like zinc can make things worse).
Things to look into maybe. I hope you start feeling better soon!