You are a week late and are wondering if you could be pregnant from unprotected sex on cycle day 8. For a 30 day cycle the most likely day of ovulation is cycle day 16. The rule of thumb is that sperm survive inside for no more than 5 days, so the chance of pregnancy is quite low. You are not telling of any other early pregnancy signs which would have been noticed by now. Run a home pregnancy test if you wish to confirm this.