I have suffered periods of insomonia my whole life and I have no way if this could apply to you but, when a period of insomonia waned, and I began sleeping longer I actually felt More Sleepy during the day. I actually found that by getting up earlier in the morning I would feel less sleepy during the day. Very weird, I know.
My natural body clock would have me go to sleep at 9pm and get up 5am for the best "rested" feeling during the day. The less I fight that time table, the better off I am. Can you indulge your inner clock for a while and see if it helps.
On the other hand, UC has just about taken care of my insominia problems the last year. Well, that and a habitual visualization program I follow at night.
Good luck. Fatigue and sleepiness/insomia have plagued me for years so I know it can be disruptive.