What Causes Persistent Fatigue And Headache?

I am 29yr. Old female. I m of avg weight and height, i eat healthy meals. I am always getting bad headaches in the afternoon and I am so tired around 4 when I get home from work I usually sleep everyday for an hour at least around this time. I go to yoga, pilates, and the gym regularly. I've had thyroid checked in the past and I'm told it's fine. Even if I don't have a headache I am always tired in the afternoon, I'm not on any medication.
Could it be some sort of food allergy I don't know about