Severe fatigue

I have struggled with fatigue for as long as I can remember. And not just normal fatigue. Fatigue like I could sleep 12 hours and still be able to sleep 1-2 hours during the day. I’ve tried shortening the amount of time I sleep at night to just 6-8 hours thinking I’m over sleeping, but that definitely didn’t help. I’ve been on B12 supplements, I exercise 4-6 days out of the week, I have a balanced diet, but I can not shake the exhaustion. I’ve had a full blood panel done, had my thyroid checked and all my “levels” have been normal aside from B12.

Anything you guys could recommend would be helpful!