I've struggled with sleep issues and fatigue and done a lot of research and experimentation over the years, so I can offer some ideas of things you may want to look into and try. The problem is that it is not a disease that can be treated mechanically, but it is the bodies response to overwhelming biological stress, and that stress can have many faces. There are so many possible causes, that it's very unlikely your doctor will be able to get to the root of it, as they simply can't spend that much time on a single patient. A lot of research and experimentation is going to be needed on your part if you want to figure out the best interventions for your case and start getting better.

First let's talk about sleep, since it sounds like it could be a major component of this. Have you had a sleep study, do you have sleep apnea or any other kind of sleep condition? I never tested positive for sleep apnea, but I know for a fact (personal experience and experience of partners) that I do sometimes have breathing disturbances at night which seem to impact my sleep negatively. There are some things you could try if you suspect the same. Ideally, you want to be breathing gently through your nose the entire night, as mouth breathing (esp. during sleep) leads to hyperventilation, which reduces blood CO2 concentration too much, which makes oxygen less available to tissues (See Bohr effect) and causes a number of issues leading to non-restorative sleep.

A few potential remedies for this are the following. Tape your mouth shut before bed, using a postage size piece of micropore medical tape in the middle of your lips [2]. It sounds crazy but many people find it effective. Or you can see about having your dentist make you a mouth guard, or just buying one off the shelf. Or (and also in addition), do breathing exercises before bed (like box breathing or Buteyko breathing), to calm the breath and get into a slow steady nasal breathing pattern.

If you suspect nighttime adrenaline and cortisol may be a problem (nightmares?), you can experiment with either eating right before bed or taking supplements. Magnesium and l-theanine would be a good combo to try. You can also try having a balanced snack before bed with carb/protein/fat, which will keep your blood sugar up during the night and prevent hypoglycemia. Eating before bed is obviously not ideal, but it can be a useful intervention to help sleep in the short term. Sodium before bed may also help keep nocturnal stress hormones low, and you can take just salt in water or have a salty snack [3].

Do you have any kind of sleep tracker? I use an apple watch and the AutoSleep app. It's not perfect, and obviously a simple wrist tracker can't accurately monitor REM sleep. However, there is a strong correlation between my sleep results in the app and things I've done prior to bed, so it's useful for tracking things at a coarse grain.

There's some research I've seen that CFS is sometimes linked to low blood volume [1], and I've personally found supplementing electrolytes to be very beneficial. I think it makes a lot of logical sense, because CFS seems to be a symptom of too much stress on the body, and stress hormones like cortisol cause wasting of electrolytes. This is also a possible explanation for your brain fog. Pick up an electrolyte powder and give it a try, there isn't much downside. Also note that most electrolyte powders have less than optimal amount of salt, so unless you have an existing condition regulating sodium, you should try adding additional salt too [3]. Some other supplements I've found useful for fatigue are a b complex, taurine, and creatine.

1) https://www.healthrising.org/treating-chronic-fatigue-syndro...

2) https://www.mrjamesnestor.com/breath

3) https://www.penguinrandomhouse.com/books/545379/the-salt-fix...