Best-case scenario: There really isn't one. It's never normal to have a flow so heavy that you have to switch tampons that frequently -- or need to change your pad at night, says Vanessa Jacoby, MD, associate professor in the department of Obstetrics, Gynecology, and Reproductive Sciences at the University of California, San Francisco.
Why it could be more serious: When your period is regular but excessively heavy, the most likely cause is uterine fibroids, tumors that grow in the walls of your uterus and affect 20 to 80 percent of women before the age of 50. They're benign, but they can have serious consequences like anemia (some women even need blood transfusions, says Jacoby), severe fatigue, and, depending on their location and size (ranging from a pea to a watermelon), they could make it harder to get pregnant and increase the risk of complications during pregnancy. Heavy bleeding can also be a result of a thyroid condition or a clotting issue, so before any treatment starts, your gynecologist will confirm that fibroids are causing your symptoms, likely via pelvic ultrasound. If fibroids are the issue, your options for dealing with them include medications, surgeries that target the fibroids but leave the uterus intact, or hysterectomy, the most common recommendation from doctors.