If the appliances are uncomfortable, that means the teeth are trying to
shift.  I would GUESS that if you stopped wearing them one night a week,
your teeth would move.  It may be related to clenching habits, or to
day-time habits (biting on a pencil), skeletal relationships, quality of the
orthodontics, etc.  End result, if you can live with the teeth moving out of
position, you can perhaps stop wearing the appliances.  Better yet,,,,,,,,,
why not go to the orthodontist who did the work, and discuss it with him?

    Good question--for your orthodontist, who will know the particulars of
your situation and how stable your result is likely to be without retention.

Steve