My periods are reg. 28day cycle, i had sex this month & pd is usually 5-6day & 1&3 spotting & 2day very lite bleedin what can be a reason? preg test

Light period.: The main reason for light periods is a change in hormone levels. Causes for what seems to be a light period can include: implantation bleeding in early pregnancy, thyroid problems, eating disorders, excessive exercise, initial periods for a girl, use of an intrauterine device, oral contraceptives ; perimenopause. Take a pregnancy test if you are uncertain if this was your actual period.