What Causes Severe Headaches Along With Tiredness Post Having Concussion?

My daughter suffered a concussion in 02/04/13 from a cheerleading accident. She has gone through vistibulary therapy. She also ending up with Post Concussion Depression. She still has headaches in the front of her head in the center and she seems to zone out when tired. She suffered another concussion on 12/13/14. She is tired a lot. She had a MRI and EEG a couple of weeks ago and they can back normal. She is scheduled to have an Ambulatory EEG next week. Do you have an y thoughts on why she still gets so tired, and has headaches.