Here is what I have learned and see if it helps you. I know we feel fatigue all the time but try to observe when does it get worse.
I am going to assume you did the basic checks already: Vit D (the 2 tests), B levels, Thyroid (t3 and T4)....
1) when you wake up is it bad? If so might be that u do not go to stage 4 sleep so try stage 4 inducer and see if that helps. See if you can get a sleep study, you have to point out to check for stage 4 (usually they only look for apnea).
2) Does it get better when you eat or worst? If it gets worst try to eat chicken broth for a few meals and see if that makes you feel better (well done and with organic chicken) this is just to see if it is tummy related. If it is food related, there is a lot you can do, allergy test, digestive enzyme if needed....
Another thing I noticed immune boosters killed me (equinacea tea puts me in bed for 2 days) Inmune mods made me feel better (acai). Foods that were vasoconstrictors made me feel better and food that would vasodilator would crash me.
I would google food name+ immune booster, food name+ immune suppressor, or food name+ immune modulating
also food+vassocontriction, food +vasodilator...
If you cannot cook, try avocado with salt and lemon. That is good and no allergenisc. Check with your doctor.
3) There are great supplements combo for energy to help: CoQ10 (as much as you need up to 1200mg) + this comes together (ALA 200mg+ acetyl l cartinine 500), 2 pills of this a day before 3pm + NAC 1000mg + D-ribose. I am not doctor this is just for you to have a start point for research, Some people say ALA is bad with fillings but I never had a problem.
4) I get inflamed, so I do OTC Aleve every 6h (whatever the bottled instructions are) until I feel the inflammation gives (Is a feeling in the head). This is just so you realize if your issue is inflammation is not good to do long term but once you know if it is your issue, you can try to find the source (mine is the food allergies).
Again ask your doctor before trying anything.
5)If you are woman, the cycle influence, before my period I get tired and nothing I can do except wait it out.
My point is if your base is a 3 or a 2. Observe what makes it a 1 or a 0. And what makes it a 4.
If you have orthostatic intolerance (HR goes up 30bpm at standing) then Try midodrine or florinef (or they natural equivalents).