I don’t know what’s causing it but my character hasn’t been able to sleep in about 5 days. The only trait I have that has anything to do with sleep is the accomplished sleeper trait, which is meant to make it easier to sleep. Not the other way around. If it means anything I drank some atomic coffee before, but that was on day 1. It’s now day 6 and I need to sleep so my HP goes up.
Atomic coffee is really powerful, but not 6 days powerful (more like 8 hours of sleep per sip).
Try taking ambien, downing an entire bottle of cough syrup (the regular one, not non-drowsy), biking for a longer while or take a dose of meth. Yes, meth - it reduces fatigue at first, but then gives it all back with a big extra.
If nothing works, debug menu has the answer: bind debug menu by going ?->1, finding debug menu entry and binding it to some unused key.
Then open the debug menu, find entry for NPC/player edit tool (I think ‘d’), select yourself, pick “edit needs” and check your exact fatigue.
If you retry the check for fatigue in 1-2 hours and nothing changes, there may be some bug somewhere that is causing it, otherwise it may be something you’re using or eating.