It usually occurs regularly, around day 14 of a 28-day menstrual
cycle. Having unprotected intercourse on last day of your periods reduces the chances of
pregnancy as the innermost lining of the uterus has been sloughed off during menstrual cycle.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps.