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Emergency contraceptives are known to cause irregular periods
as a side effects.
If you have not had unprotected sex after 16-1-12 then there will be no chances of getting pregnant.
In case you have had sex then if the pregnancy
test is negative then to confirm whether you are pregnant or not you should get a blood test
called Beta HCg
If that test is negative then you should consult a doctor and get a medicine prescribed to regularize your periods.