What Causes Dull Headache On The Forehead?

Hi- This is about my 8 yr old daughter. She has been having these dull headaches on her forehead and temples since few weeks, on and off. She is short sighted, very strong prescription, -5, I took her to eye doc who ruled out any change in strength and then we took her to pedi who checked her and everything seemed normal, even got her xrays that look normal...so am wondering what could be causing these and what can we do for her to get better. Her pedi said everything looks normal, but if this continues for couple more weeks then we can get an MRI done, just to rule other things out....he said it could be allergy related as well sometimes kids get it and then get over it.