The most common reason for having two periods in one month is when a woman has a short cycle and one period occurs at the beginning of the month, and then about 24 days later, another occurs at the end of the month, according to U by Kotex. However, if a woman's cycle is 30 days or longer, any added stress or change in daily life can cause this disturbance.
According to She Knows, stress, diet, exercise, birth control pills and drinking too much alcohol can cause changes in the hormone levels of a woman and affect her menstrual cycle. Additionally, if pregnancy is possible, the second period, if lighter than usual, could be a sign of implantation bleeding, which occurs when a fertilized egg attaches to the uterine wall. A pregnancy test should be taken to rule out or confirm pregnancy if this is a possibility.
If bleeding is heavier than usual or accompanied by excessive or abnormal cramping, it is important to visit a gynecologist to rule out other conditions that may be affecting the menstrual cycle, according to Dr. Northrup. Common causes of excessive menstrual bleeding include fibroid tumors, adenomyosis and thyroid problems. In some cases, a cause for heavier and unusually frequent menstrual bleeding cannot be established.