Thank you for your query.
The reason for your abnormal bleeding is because of the emergency contraceptive
These are hormonal
pills, and often induce a withdrawal bleed after consumption.
That is the most probably reason for the bleeding.
Other causes for post menstrual spotting are cervical lesions, polyps, fibroids, endometrial thickening etc.
If the problem recurs, I would advise you to consult a gynecologist.
meanwhile, ensure that you use a reliable and permanent method of contraception
in the future, as emergency pills are not meant for regular use.