If you have sex during your menstrual cycle and do not use birth control, there is a possibility of pregnancy. The probability of pregnancy during safe intercourse is about 15%, and if you do not use birth control during ovulation, it is about 60%-70%. You can use a pregnancy test more than 12 days after intercourse, or come directly to the hospital to take a blood test for HCG to rule out the possibility of pregnancy. In addition, if pregnancy is completely ruled out, there is also a possibility of endocrine disorder or abnormal ovulation, or even delayed menstruation or amenorrhea due to non-ovulation. It is recommended to do an ultrasound examination. If the uterine adnexa are normal and the thickness of the endometrium is moderate, progesterone can be added in appropriate amounts to promote menstruation.