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The ECP will help in preventing pregnancy if you have taken the ECP within 24-48 hours of the unprotected intercourse. Since the emergency contraceptives contain high doses of hormones, these can disrupt the normal hormonal and period pattern. Wait and watch for your next periods which can be delayed. If pregnancy is suspected look out for development of any new symptoms, and consider visiting your doctor/gynecologist at the earliest for thorough examination (to confirm pregnancy related changes/signs in body) and blood/serum HCG level test (to confirm/rule out pregnancy accurately) if periods do not start within 10 days of expected period dates.
If pregnancy gets ruled out, further investigations would be needed to look for the underlying cause for your absent periods. Get started on treatment as indicated by your examination findings/investigation results to help you regulate your periods.
If pregnancy gets ruled out, and if you are not ready for pregnancy, but intend to remain sexually active, consider visiting your gynecologist to get started on suitable regular birth control measures to be protected (after your periods). Be regular with birth control use as instructed. Avoid having unprotected sexual contact.
Take care.