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After taking emergency contraceptive, bleeding results in next 5-7 days. If this does not happen or you do not get your usual periods, then you should consider getting a thorough check done to make sure there are no other underlying problems for your absent periods. Having irregular periods could be due to many reasons, do not be afraid of taking help from a gynecologist to solve your problem. Emergency contraceptives work if taken within 72 hours, so do not worry about pregnancy.
You might need to get hormonal levels and blood work-up done along with ultrasound scan to look for causes like thyroid problems, PCOD and other hormonal imbalances that could be reason for your absent periods.
Take care.