What Causes Spotting Instead Of Period?

im 34 years im 5'3 and i weigh 57 kg , i have been stotting since 31 july and my period was do on 4 augest , but there is nothing but spotting some times pink ,brown . my period is always on time every 28 days ,my last period was on 7 july and ive had unprotected sex on 19,20 , and 21 of july ...im still spotting light bleetng only when i wipe its the 7 of augest and no period