I used to suffer like this and adjusted my diet. I now take multi vitamins and Omega 3 capsules. I reduced my coffee to 2 cups per day and take in plenty of water. Seems to have done the trick, but I still need at least 9 hours sleep a night!
But if you are suffering any other symptons other than being drowsy you should go have a check up with your doctor. In fact if you are worried at all go for a check up.