A few things....I am almost a year sober and sleep is a big deal for me. It was a HUGE thing in my first months (I am 345 days sober today) and I slept a LOT.
It evened out mostly and I was taking a nap some days of the week. In Dec, I went on an antidepressant (added to my other drugs which does include seroquel for sleep) and it knackered me for a good number of weeks, probably 4-5. I HAD to lay down with very sudden onset and was napping for a couple hours at a time, or even about two hours after I got up. That has evened out and now I nap some/most days for shorter periods of time and they work around work, meetings etc- so one question for you is if you are on any psych drugs?
Are you dreaming or having nightmares? Any other symptoms (sweating, etc)? I ask because I went through all of that and did get some help from my psych in terms of adjusted meds.
Can you exercise? How are you eating? I understand very well what you are saying about the overwhelming nature of this kind of sleep thing. Perhaps even though the tests you've had are normal, it's worth discussing what's going on with your dr.
Take care of yourself.