Always Hungry and Tired?

The past couple of weeks I've just been feeling exhausted. I'll go to be around 10 every night and wake up at 7 but still be tired all during the day, sometime I have to go to bed earlier because I'm so tired or take a nap! I sleep all the way through the night and dont have disturbances. I am also always hungry, nothing I eat will flll me up. After having a big meal like lunch or dinner, less than an hour later my tummy will be rumbling. I'm a normal weight and eat a healthy diet, I havn't changed anything to do with my lifestyle that has stressed me out or anything like that. Does anyone have any idea what it could be :S Thanks xxx