Hope this is okay if I just focus on the thyroid because I had undiagnosed thyroid for many years . . . my tests all came back normal until I started cycling between over-, normal, and under and then back again . . . the episodes drove me to the ER with many of your symptoms. When underactive, I was like a slug and when overactive, I ended up in ER because of the symptoms. Long story short, finally diagnosed and received treatment which made a whole lot of difference.
Couple of things you need to be aware of . . . First, thyroid issues can run in families . . . . an elderly relative told me that several members of her generation had the same symptoms (of course, back then, not called thyroid issues). In fact, if there are other members of your family with thyroid issues, then you need to insist on more in depth testing. So, find out and write down who in your family has thyroid issues.
Second, family doctors are not always the best with thyroid tests. I was fortunate. I had a new doctor who told me that the blood tests were normal (I had them when I was in a normal phase), but he insisted on asking me how I felt (wow! what a great doc). He felt that the blood work was not revealing what was "wrong" and he referred me to an endocrinologist who specialized in thyroid issues. She insisted that I have an open requisition which meant that as soon as I felt that I was going into an under- or overactive episode, I was to get bloodwork. The trick worked as she had ordered full antibodies testing and was able to see that I had both types of antibodies (for Graves and Hashimoto) and that the cycles were becoming more compressed and intense. Finally, there was a firm diagnosis and treatment even though it took over a year. In fact, the doc suspected that I always had thyroid problems but that the episodes were so far apart and the blood work normal that it went undiagnosed. I know that you are fatigued, but insist a consultation with a specialist in thyroid or perhaps there is a teaching university nearby that may have a program.
Third, because thyroid is more prevalent in females than males, some docs do not pursue a diagnosis of thyroid. I hate to think that there is this short sightedness, but there is. I have two male friends both of whom deal with thyroid issues very effectively through medication.
Fourth, you have to be your own advocate. Find a doctor who listens. I hope that endocrinologists who specialize in thyroid disease are not the ones blowing you off. I don't know where you live (UK?), but see if you can contact a local thyroid association for a list of doctors specializing in thyroid. Did your sister see a specialist? Or was it evident from her bloodwork that she had a thyroid issue? In any case, as fatigue and frustrated as you might be, insist on a specialist who will run as much thyroid blood work as possible.
Fifth, know that you are not alone . . . thyroid is an awful disease as it affects metabolism which affects brain chemistry and every other function in our bodies but it is very manageable through medications . . . .
Please keep in touch and let us know how you are doing . . . and, by the way, thyroid does not care if you are 6'6" or a petite 5' 4" . . . . you are showing so much strength in this fight because your medical support system appears to be failing you in a very huge way . . . including anxiety . . . .please, please keep up the good fight . . . take care, KC