The normal menstrual cycle is 21-35 days, and a difference of 7 days before and after each period is normal. If it exceeds this range, it is irregular, which means that the menstrual cycle may be shortened or lengthened, which are not normal. The most common causes are endocrine disorders, which means no ovulation, sparse ovulation causing irregular vaginal bleeding, sparse menstruation, and frequent menstruation. Therefore, if you have irregular menstruation, you should check sex hormone 6 and thyroid hormone on the third day of your period to see if it is caused by endocrine abnormality, and you should treat it according to the endocrine test results.