after brith of my newborn baby

MY BABY WAS BORN 01/14/09 AND I BLED TWO WEEKS AND STOP AND I BREASTFEED FOR TWO WEEKS AND I HAD SEX. BUT I DID NOT COME ON 02/09/ NOW IT IS 03/09 AND DID NOT HAVE ONE YET. MY BABY IS 7 WEEKS OLD I TOOK A PREGNANCY TEST NEG THIS WEEK. HOW LONG DO IT TAKE BEFORE YOU GET YOUR PERIOD AFTHER BRITH.