There are many factors that can cause a sudden low menstrual flow, excluding pregnancy, which may be caused by the following factors: 1. The patient may also suffer from gynecological diseases, such as endometritis, pelvic inflammatory disease, etc. 3, it is also possible that the recent stress or overwork, affecting their endocrine function disorders, resulting in the symptoms of low menstrual flow. 4, and their own malnutrition also has a certain relationship, such as irregular diet or excessive dieting, can lead to malnutrition, resulting in the symptoms of low menstrual flow.