According to WebMD, it is possible, though not standard, for a woman to have her period twice in one month. Because of the additional blood loss, this problem is sometimes accompanied by anemia. Causes of frequent periods include weight changes and hormonal, thyroid issues and physical issues.
WebMD indicates that stress or a large weight gain or loss sometimes triggers irregular periods. They are also brought about by changes in hormonal levels, such as when certain birth control methods are switched. In addition, hypothyroidism --an underactive thyroid-- or uterine, cervical or vaginal abnormalities occasionally lead to menstrual anomalies. Treatment is often required, so a woman with twice-a-month periods needs to schedule a pelvic exam with her doctor.