Thanks for the query to ATD for an opinion,
Ideally after taking plan b on 3rd September post sex, you should be getting your withdrawal bleed within next 7-10 days, i.e by 10th-13th September.
If you did not get the bleeding then there are chances that you could have been pregnant. Again after taking plan b on 24th and yet not getting a withdrawal bleed calls for an urgent serum beta hcg test to rule out pregnancy conclusively. If the hcg levels are more than 3mIU then you are pregnant for sure, else you may wait for another week for your menses to return naturally.
Further course of oping for a withdrawal bleed with progesterone's can be contemplated if menses still do not return after a week in case of absence of pregnancy.
So please get a serum beta hcg test done.
I hope i have answered your query in detail,
Wishing you safe sexual practices,
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.