Why do I have headaches all the time?

Headaches can have causes that aren't due to underlying disease. Examples include lack of sleep, an incorrect eyeglass prescription, stress, loud noise exposure, or tight headwear. Often, headaches are triggered by lifestyle or environmental factors such as stress, changes in weather, caffeine use, or lack of sleep. Overuse of pain medication can also cause a constant headache. This is called a medication overuse headache or a rebound headache.

Explanation:

chemical digestion occurs in the stomach were hcl and pepsin forms chyme, the mouth in which salivary amylase breaks down starch to form bolus, and the small intestine specifically the duodenum.