I'm 16 and i started my period im not supposed to start my period until next sunday ?

Irregular menses: Irregular menses are very common in teenage women, commonly due to anovulatory cycles. If the lack of regularity is bothersome, ask your parent/guardian to take you to your Family Doc to discuss use of hormonal contraception (yes, birth control) to regulate your periods. Your options include pills & shots, although other options are available as you get older (check out PP's http://goo.gl/2QKlgt).

Not always on schedu: This is not usually serious. Timing can change. You physician can have you see a gynecologist who can better clarify but many things can change the timing of the cycle