4. 4 years baby suffering from headache.

My daughter is, 4.4 year's old. She is suffering from headache from her 2 years old. She complains headache just only the center of the forehead. Else no other part of the head. She complains it for 4-5 sec. After that she told that is resolves. No medicine needed. No crying or hesitation while she has had headache. From her age 3.2 years she stop to talk about headache. But from the middle of the September this year she again told about headache in the same place of the forehead. We have done ct scan, EEG, whole abdomen usg, PNS Sinus test, lft, crp, cbc. All test reports are normal. But the pain is still around. What should we do now?? What is the reason behind it?? She says about headache in any time of the day. But she has no vomiting or nausea with it. But she has too much gas problem and from her 7 days of age she has problem of constipation. But constipation problem is now very much sorted. Pls give me some suggestions and reason behind her headache. I am too much worried