On and off headache for weeks. it's mild but also get sudden chills that last for seconds. i don't have infection. what could be the cause ?

See a doctor: Intermittent headaches need to be better defined (location, precipitating factors, associated symptoms, etc.), and chills may indicate the body's mechanism for increasing body temperature which may be low at the time the chill occurs. If you have had dental issues or questions about pulmonary or intestinal infection previously think about extension to the head. See a professional and be evaluated.