Just what is wrong with me ?

As most of you who read this will know, my great passion in life is orienteering and just at the moment I don't seem to have the energy to do any !

Raced on the South Downs nearly a month ago now and had a great time ( follow my route here ... find course M60 S down the side where it says 'choose class or course'and click my name now click at the bottom on 'view routes' and 'view animation' ... start the animation... enjoy). Got home and was so tired had to go to bed immediately and that is it really ... just have not recovered. Doctor has done all the usual blood tests and says that they are fine. Some days are okay but others are spent just trying to get moving ... no energy at all.

Any suggestions ( that can be posted)?