Hi, thanks for using healthcare magic
Most emergency contraceptives , including this one, work best if taken within 72 hrs of unprotected intercourse
which would have been by the 14th. It may still have an effect but the efficacy is decreased at this point.
It is possible that you did not conceive.
It would be best to consider another form of birth control other that withdrawal which is not considered one of the most effective methods. The methods are oral contraceptives, injectable contraceptives, IUD, the patch, condoms.
I hope this helps