dj:
Sounds pretty similar to my situation...
Anyway, I noticed it's slightly better when I'm really strict about my sleeping pattern. So what I'm trying now is making sure to get at least 8 hours sleep and so far it seems to work. Means I don't get a lot done during my work week (I'm on a 6 days on, 3 days off pattern) but feel not so burned out on my 3 days off either so I can make easily up for it.