When you do check your thyroid, do check it completely: free T3, free T4, TSH, anti-bodies, the whole shebang.
I have had autoimmune thyroid disease since childhood. I am hypothyroid. I have both Hashimotos Thyroiditis and Graves Disease antibodies, and I have Thyroid Eye Disease.Well, there are many who are not that fortunate to finally find the cause of their CFS-like illness. But you do need to check the thyroid properly.
I spent 20 years misdiagnosed with fibromyalgia/ME/Chronic Fatigue Syndrome because my blood tests showed "normal" thyroid levels. Since taking thyroxine, I have been cured.
Hypothyroidism caused me to develop severe food intolerances, which I managed for several years with the "Failsafe Diet", a diet free from additives, and low in salicylates, amines, and glutamates.
I have Attention Deficit Disorder (much improved by thyroxine), and I used to have Asperger's Syndrome, (resolved by thyroxine).
I am gluten free, and eat a low carbohydrate, additive-free, moderately low salicylate diet.