Many of the headaches are due to Stress, eye strain, sinus blockage or even Migraine. Very rarely it could be due to something significant like a stroke or tumor. Take mild anelgesics with Antacid and rest. If the headache is progressively increasing or associated with vomiting or double vision, you need to consult a Neuro Specialist and possibly an MRI scan of the brain may help to clarify the issue.