Hi welcome to Health care magic forum. Head ache is a vast subject could be due to tension to tumers in the brain. Of course intracranial tumers and intra cranial pathologies are excluded by M.R.I.
It could be migrain, sinusitis
, upper respiratory infections, or some chronic infections, and the most commen anxiety
I advise you to consult a neuro physician for diagnosis and treatment. If he fails you can approach E.N.T.surgeon for diagnosis and treatment.
Besides i advise you to follow some diet recommendations as avoid taking more of spices, chillies, junk foods, and oily foods as these can irritate gastric mucosa
and nervous system .
Wishing for a quick recovery and thanks for calling.