Started my period on the 3rd ended the 8th but still spotting it is now the 15th last time i had sex was protected and on the 15th of last month why ?

Multiple causes: Spotting can be random or a sign of something more serious. For a 20yo, the chance of something serious, ie cancer, is very unlikely. The two most common causes are 1)side effects of birth control and 2) infection. If you have started a new birth control, whether pill or IUD or other, give it two months for your body to adjust. If not, see a gynecologist.