Always sleepy....why?

For some reason, lately if I sit still I fall asleep....I also can barely get out of bed in the mornings. As soon as I get my kids situated and get some housework done I end up back in the bed, sleeping. I know I'm not pregnant....I have 3 children so I'm pretty aware of the signs/symptoms. Does anyone know what could be causing this? SN: I sleep 8 to 10 hours a night.