Hi liksani,
I too have recently had that really exhausted feeling. I went and had my blood work done to rule out thyroid or low iron problems. Since everything looked fine medical-wise, I finally had to realize that the tiredness was due to overtraining. I've slowed down a bit and feel better.
My advise would be to rule out any medical problems first, then go from there.
Good luck and feel peppy again soon!