B2.
A little over a year and a half ago my fatigue worsened (it's been 33 years dealing with CFS). So with the benefit of more user-friendly insurance, I started pressing to see if there were any co-factors that could be contributing to my fatigue.
Among the things that were sub-optimal were my thyroid levels. FT4 was in the "normal" rage, but at the bottom of "normal." TSH was also "normal" but in the top of the range (depending on what accepts as a "normal" range).
If I wasn't feeling knackered I'm not sure the very conservative Endocrinologist I saw would have treated me. But I "self-advocated." It has been almost a year of slowly raising the dose of levothyroxine. I think I may have finally hit the "optimal" dose of 137 mcgs in the past weeks.
Optimizing thyroid levels has been helpful to me (but it has not solved CFS).
My symptoms have been mostly fatigue, brain fog, unrefreshing sleep, PEM, and in the earlier "viral-like" early phase symptoms included night sweats, swollen glands, photophobia, and crash-inducing chemical sensitivities (tobacco smoke and acetone being especially bad culprits). I've never had unexplainable muscle or joint pain, GI issues, or POTS.
Bill