I'm always tired.

I have a tiring lifestyle, I have to travel a lot to college, do a lot of walking and a lot of mentally tiring aspects to my days. I work on a Saturday but all I want to do is sleep and I can't ever be bothered to do anything.

If I have a nap, I wake up feeling more tired than I did before I went to sleep!

I have a very good, varied diet.

What is wrong with me? Is there a physical defect or am I just lazy?