It is normal for women to have a period of 3-7 days, which is a relatively normal range. If it is more than 7 days, half a month long, or a short period of 2 days, it is a case of irregular menstruation. The reasons for this are as follows: 1. The main reason is that the menstrual period is relatively short, mainly because the female uterus is not fully developed, resulting in less menstrual flow and painful menstruation. 2. Endocrine abnormalities exist, and if you stay up late for a long time or have poor health, this can lead to endocrine disorders and affect the menstrual flow. 3. 4. It is possible that the menstrual period is short after an abortion or a scraping operation.