Im 21, my period only lasted 2 days and it usually lasts 4 days.. my period has stopped but still have tender breasts ect. can't be pregnant i'm a vir?

Light Periods: The main reason for light periods is change in hormone levels. Causes for what seems to be a light period can include: thyroid problems, eating disorders, excessive exercise, initial periods for a girl, use of an intrauterine device, oral contraceptives, perimenopause & implantation bleeding in early pregnancy which rarely occurs.