M.L.
Wow - I was going to pose this same question today. I've gotten to the point I've started thinking I have some serious issue - like lupus or something. Reading the responses I am going to try vitamin D for awhile.
A couple of years ago I thought something was going on - went to my dr. and they even did blood work, etc. everything came back looking fantastic (they were looking into thyroid issues - which runs in the family) - only thing that came back is that the GOOD cholesteral in my body is high - so I thought, Wow, only thing blood work is showing is that I should be feeling great, but I'm not - that's depressing!!!!!!
This past year has been stressful for me and I ended up seeing someone for depression.......was feeling great however still feel exhausted ALL of the time........best of luck to you - hope we can kick this issue!