Have you had your thyroid, B12 , vit D and iron levels etc checked?
Assuming they are all normal, and your diet's ok generally, then it could well be hormone related. Do you take hrt? I know it's a personal choice, but for me, taking hrt and then the pill was the only thing to stop the crushing fatigue. Took several months, but these days it's nothing like that scary, strikes anytime 'what the hell is wrong with me?' fatigue. I've also worked out that high progesterone affects me as much as low estogen when it comes to fatigue.
Big hugs - it's a horrible thing xxx