The first thing you need to do is to check if you are pregnant, and after you have ruled out pregnancy, you may be having irregular periods. 1. Pregnancy: If your period is delayed for more than seven days after you have had sex, you can use a pregnancy test to see if you are pregnant if you have two bars, and if you have one bar, you can temporarily rule out the possibility of pregnancy. If the period is short, you can go to the hospital to take a blood test for HCG to be able to diagnose whether you are pregnant. 2. Irregular menstruation: If your menstrual period is delayed for more than seven days, you can rule out the possibility of pregnancy, and then you are considered to have irregular menstruation. It is necessary to regulate menstruation under the guidance of the doctor, such as taking progesterone capsules, taking three days or five days, after stopping within seven days will come to menstruation. The delay in menstruation after sex, need to go to the hospital after a clear diagnosis, under the guidance of the doctor to deal with.