Re: thyroid - you will find that most doctors don't really understand thyroid issues and rely exclusively on the standard tests (tsh, uptake, etc.). Radiation to the neck area will almost always have effect on the thyroid gland (the radiologist report described mine as "incredibly tiny"). The real test of whether your thyroid levels are OK is how you feel, irrespective of the test results. And, the usual thyroid supplements (Synthroid, Levoxil, etc.) include only the T4 component. Armour Thyroid (a natural vs synthetic product) contains both the T3 and T4 comnponents. The synthetics rely on the pituitary gland to convert T4 to T3, so if there are pituitary problems, it doesn't happen or doesn't happen in sufficient quantities. There is literature available out there that discusses thyroid issues, including fatigue.
I am 4 years out from end of treatments. All subsequent tests (PET, CT, MRI, blood work) have shown no cancer. The fatigue continues and seems to have gotten worse in the last few months. My GP prescribed Ritalin, but it had no effect. Further research suggests supplementing with testosterone (Androgel, etc.) so I'll discuss that with my GP later this month.
Most importantly, don't give up, don't lose hope, and continue to work with your docs (you may have to "lead" them regarding thyroid), but remember the three most dangerous words in medicine....."you're the doctor".