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Headaches can be related to the hormonal changes due to monthly cycles.
Headaches that occur just before and during menstruation are often due to the drop in estrogen that occurs at this time.
There are many reasons for headaches. They can occur due to tension and stress of course, as well as things such as vision problems, elevated blood pressure, low or high blood sugar, and other metabolic problems.
If you are otherwise healthy, and find that a headache is occurring consistantly before or during each menstruation, this will of course point to a hormonal cause.
Besides the Midol and Tylenol, consider taking a nonsteroidal anti-inflammatory drugs (NSAIDs), such as naproxen (Aleve) or ibuprofen (Advil, Motrin).
You can also try holding ice to the area of forehead or area of pain, if possible (since yours is behind the eyes holding it to the area of pain may be difficult) which can sometimes help to relieve it. Conversely, some find a warm bath helpful in alleviating headaches.
If your headache will not relieve; keeps you from sleeping; or is higher than a 5 on a 1 to 10 scale of pain consistantly, you will need to be evaluated.
If the headache does reoccur monthly, you will also want to notify your physician as there are interventions that can be done to prevent hormonal headaches.
Please reply if you have any more questions about this.