The chances of pregnancy
in your case is nil since you had sex during the last time of the periods and not 14 days prior to it which is the fertile period for having baby.
The withdrawl bleeding is normal and the irregular bleeding may occur after you take the pill.You may wait a week and have the serum hcg
test and uterine sonography
done if your period doesn't come within a month to rule out pregnancy.
The chances of having pregnancy are very very less in your case since you also took the pill within an hour after sex.