How far along are you? I understand it's natural to be really tired in the first trimester and that it tapers off after that. I've noticed that with myself.
Are you at home alone all day? Maybe some of your fatigue is coming from boredom? Try taking a walk every day or just trying to get out of the house for a bit.
If you are concerned, or if you feel like all the sleeping you are doing is affecting your health in any way, maybe you should speak to your doctor. For all I know, he/she could tell you it's perfectly normal and to sleep all you want! Lol