The reasons for not having menstruation all the time after sex include pregnancy, mental factors, disease factors, drug factors and so on. It is recommended to consult a doctor in time to identify the causes and treat them under the doctor’s guidance. 1. pregnancy: women of childbearing age, have sex, if there is a delay in menstruation, first of all to determine whether pregnancy, you can use the early pregnancy test paper test, you can also go to the hospital for blood HCG and ultrasound examination. 2. Mental factors: such as mental tension, anxiety, depression, etc., can affect the function of the hypothalamus and ovaries, resulting in delayed menstruation. 3. Disease factors: premature ovarian failure, polycystic ovary syndrome, hyperprolactinemia and other diseases can affect the hypothalamus-pituitary-ovarian axis of neuroendocrine regulation, which can also lead to delayed menstruation. 4. Drug factors: long-term use of contraceptive pills, diet pills, may disrupt the hormonal balance in the female body, thus delaying the phenomenon of menstruation. There may also be other reasons, it is recommended to go to the hospital in a timely manner to clarify the cause of treatment.