Having sex may sometimes make your period appear to start earlier, especially when your period is already due. During orgasm, uterine contractions may occur, potentially helping menstrual blood flow if menstruation is about to begin. However, sex does not reliably trigger an early period or change your menstrual cycle. Light bleeding after sex can also result from friction, cervical sensitivity, or other causes. If your period is late, consider taking a pregnancy test. Consult a healthcare professional if bleeding is unusual, heavy, or accompanied by pain.