I got my period 1 week ago. me and my boyfriend had sex and then i started my period. i don't know why i've had 2 periods this month?

Not 2 Periods: You have bleeding after sex. Not another period. Bleeding comes from trauma, infection, STDS, or hormonal problems. It is not normal.

BCP's/ bleeding: Today's birth control pills are very low dose. If taken at a variety of times and not a constant time each night within an hour of the previous day's time, bleeding can occur especially noticable after sex, with contractions of the uterus whicn accompany sexual relations. Try to take the pill at about the same time every evening. Remember, all "bleeding" is not a "period".

Not clear: I assume you mean you had sex a week after you had your period and began menstruating again. Did you use any contraception? If not I would advise doing a home pregnancy test. If negative repeat in a week.