Many with CFS or related fatigue can have adrenal or thyroid problems. Usually a normal doctor won't interpret results correctly. That's if they even order correct tests to begin with!
Saliva cortisol testing and hormones are a good start. A naturopath can order these and interpret them well to see if theres problems with your adrenals. Cortisol is an essential hormone for life and function.
Thyroid tests can be "within lab ranges" yet not be at a "good range for your body." So again, having a great naturopath familiar with this, can help order and interpret correct thyroid tests.
Two essential things to rule out for EVERYONE with CFS.
After that, we then have tests for vitamins and heavy metals. Iron levels. Vit D is an ESSENTIAL test for EVERYONE who comes across this thread on the internet and forum. Vit D is one of the most important things for functioning and immune system and should be near the upper end of the reference range.
Leaky gut tests and bacteria in the gut.
Many with CFS have some pretty horrible symptoms, and have gone on to get Lyme disease tests, with many coming back positive, and the diagnosis being changed.
Do as many tests as possible and make sure all are treated and in optimum functioning ranges. There's no point not treating or fixing something, that can be treated or at least lessen the symptoms.
Just a starting point for all with CFS. Then you can move on to other tests and possible causes. Nobody should just accept the diagnosis and leave it at that.
To improving health, and lessening symptoms.
Newly registered contributer/member, but long time lurker/reader.