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If you have taken emergency contraceptive pills (ECP) within 24-48 hours of the unprotected sexual contact, it should work in preventing pregnancy. Since it contains high doses of hormones, it can disrupt your normal hormonal pattern, and cause bleeding and period abnormalities. Withdrawal bleeding usually occurs after about 5-7 days of taking the ECP which could be the cause for the bleeding you experienced after taking ECP. Wait and watch for your next periods/withdrawal bleeding which might be delayed. If you suspect to be pregnant, look out for development of symptoms suggestive of early pregnancy. Visit your gynecologist/obstetrician for further evaluation and management.
Take care.