I spent the majority of my late teen years constantly fatigued. I too, was concerned that it might be M.E but I think it's more to do with lifestlye and diet. If you go to sleep past one or two am the body doesn't get enough 'good' sleep associated with the REM (Rapid Eye Movement) stages. The same problem is caused by alcohol. Thus, if you have consumed a fair amount of booze and/or gone to bed in the small hours, you will not wake feeling refreshed, even if you get say, ten or eleven hours sleep and don't get up until eleven or so the next morning! I always find that if I wake up very late I feel crappily fatigued and seriously lacking energy.
Also, I started exercising regularly, (an hour of swimming 3-5 times p/w) and found that my energy levels soared. As little as 30 mins of exercise 5 times p/w is enough to get those endorphines pumping. It was also suggested that I take multi vitamins (they are cheap enough in Boots) which contain all the essential vitamins (plus iron) you may be lacking. Also try to include more oily fish and spinach in your diet for added protein and iron.
The obvious problem is that you are simply not getting enough sleep! I read that teenagers need more sleep than any other age group, so maybe try going to bed before eleven at least a couple of nights a week.
Good luck (and sleep tight!).