When you take the pill, it causes bleeding irregularities when you first start using it.
YOU would not have a miscarriage 1 week after sex, you would not even technically be pregnant yet!
Pregnancy is not a BAM, instant thing, it is a 12-14 day process of fertilization and implantation.
You likely did not have a miscarriage, but you likely do just have abnormal bleeding patterns, which the pill will help with after a few months =)