Why do i have headache for past 3 days ?

You get the most from this site when you provide detailed background information on your problem followed by a clear related question. Here there is no past history, no description of the headache, no description of measures to help, nothing. You are welcome to start over and give us some data to work with.

Since most people experience headaches at least once in their lives, it is not feasible to provide any clinical correlation with a solitary statement of "have headache". If you wish for a thorough appraisal, schedule a virtual consultation with one of our superb clinicians.(www.connect@healthtap.com)

It is not feasible to provide a meaningful opinion without additional history, and physical examination. The dry air in winter may be dehydrating you. Drink enough water daily so that your urine is mostly colorless. for the short term you may take paracetamol, no more than 3 g in one day, no alcohol. Wish you good health!