Can implantation occur after you have had your regular periods and sexual activity occured 14 days before periods.

Pregnancy: 14 days prior to menstrual period is probably around the time of ovulation, so implantation is is possible in right situation.

Very unlikely: Implantation usually occurs 6 days after fertilization of the egg. The egg is fertilized while it is in the fallopian tube and over the following 6 days, the developing zygote travels down into the uterus where it implants into the built up tissue lining the uterus. This would occur ~6 days after conception. When menstrual bleeding occurs this lining of the uterus is shed.