Further to @Coggles77 comment I would like to add that the specialty best suited to diagnosing you will depend on what your most troublesome symptom(s) are. If you have a lot of muscle pain - rheumatologist. Flu like, respiratory or allergic symptoms - immunologist. Syncope and autonomic symptoms - cardiologist. And so on. But each of these specialties will first try to diagnose you with whatever it is they specialise in, not ME/CFS. Which could be helpful or harmful, depending. Obviously you want to rule out treatable causes but at the same time, most people with ME/CFS meet the criteria for at least on of fibromyalgia, MCAS, POTS, etc. That doesn't mean you have that disease instead of ME/CFS but rather that there's an underlying cause of the whole lot that scientists haven't identified yet.