Stress?
Lack of sleep?
Hunger?
Weather changes?
What have you most recently eaten?
(Foods that can triggger headaches: avocados, chocolate, peas, pork, sour cream, nuts, peanut butter, and/or yogurt)
The medication one is usually under the case of nitroglycerin(generally used for angina. Commonly found in with people who have COD[Coronary Artery Disease], which is narrowing of the blood vessels that supply blood to the heart.)
OR
ibuprofen or acetaminophen (basic painkillers which contain caffeine so basically a withdrawl issue)