The pain you're probably dealing with: A menstrual migraine.
Two to three million women deal with this pain, brought on by hormonal fluctuations. The symptoms are no different from those of a typical migraine: intense pain usually on one side of the head, nausea, an aversion to noise and light, and sometimes visual auras (like flashing lights). An episode can last from a few hours to a few days.
While it's the drop in estrogen that occurs right before your period that sets off menstrual migraines, the pain can hit anywhere from two days before menstruation to three days afterward.
How to find relief: One or two days before your period's due to start, try an over-the-counter (OTC) pain reliever, like aspirin, or a nonsteroidal anti-inflammatory drug (NSAID), such as ibuprofen or naproxen—even if you don't yet have a headache. "Take the medication three times a day," says Dr. Green. If you can't estimate when the pain will begin because your cycle is irregular, or the OTC meds don't seem to help, ask your doctor about a triptan drug, like sumatriptan. When taken as soon as you feel symptoms, triptans do double duty, shrinking swollen blood vessels in the head back to their normal size while also blocking nerve impulses that transmit the pain signals.
If you are currently taking an estrogen-progesterone birth control pill, consider skipping the placebo week. "Keeping hormone levels continuous throughout the entire month may help keep menstrual migraines away," says Dr. Green.