After taking an emergency contraceptive, the withdrawal bleed generally ensues within 5 days of pill intake and chances are that if you have taken in 3rd week of the cycle then you are likely to pass clots sometimes. It is unlikely to be a gestational sac or abortion if that is the concern because in case you have been pregnant you wouldn't have had the bleeding at all.
I hope i have answered yorr query,
wishing you good health,
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