Light period lasting roughly 12 hrs. bright red watery.no clots. breast tenderness nausea diarrhea and severe headache. hpt neg. what could it be?

Potentially migraine: The symptoms you describe are not unusual for a menstrually associated migraine. In many women the shedding of the uterine lining can wax and wane, you may start to bleed again soon. if you recently started a hormonal birth control or had an IUD placed, that will affect the length and quality of your mentrual bleeding. That said, Sexually transmitted infection is always a concern.Consider GYN eval