Fatigue

I thought I'd start a thread for this. Anybody else having to deal with fatigue? I don't mean just feeling kind of tired. I mean overwhelming exhaustion.

I'm trying to figure out what's wrong with me. Medical doctors spend five minutes with me, tell me to get more sleep and lose weight, then it's on to the next. I certainly get enough exercise. I do karate several times a week. The sensei who just transferred to our dojo thinks it's time that I test for my next rank. I agree. But with the constant exhaustion I feel (I've been falling asleep at work, too), I don't know if I'd last through the test. At my level they can be 4-6 hours of strenuous exercise.

So that's where I am. I welcome input.