Why you got your period twice in one month may be related to having a short menstrual cycle. When the time between one period and the next is less than 30 days, it is possible to have two periods in the same calendar month.
Your period may also come twice in one month due to stress, anxiety, weight loss or weight gain, intense exercise, birth control use, hormonal changes, uterine fibroids, or polyendocrine metabolic ovary syndrome (formerly know as PCOS).
Injectable birth control (Depo Provera) can also cause bleeding that may be mistaken for a period. In some people, this type of bleeding tends to improve with continued use of the medication.
See a gynecologist if this happens often or if your menstrual cycles are shorter than 21 days. They can identify the cause and recommend the most appropriate treatment.