I know you asked specifically not to be armchair doctored but here it comes.
How sure are you that you don't have sleep apnea? Did you actually do a study? Everyone I talked to didn't think I had it but I did a study anyway and lo and behold... no matter how much sleep I got, no difference whatsoever, always tired, just like you. But now several years later I did another one and I don't have it anymore. I think if you have it at a particular threshold they might not always diagnose you with it. So if you have a "mild case" like me you might meet the threshold one night and not the next.
How sure are you that you don't have sleep apnea? Did you actually do a study? Everyone I talked to didn't think I had it but I did a study anyway and lo and behold... no matter how much sleep I got, no difference whatsoever, always tired, just like you. But now several years later I did another one and I don't have it anymore. I think if you have it at a particular threshold they might not always diagnose you with it. So if you have a "mild case" like me you might meet the threshold one night and not the next.