I am not a doctor. If you suspect you are pregnant, you should go see an OB/GYN. That said, implantation can occur up to two weeks after fertilization, which itself can occur up to two weeks after intercourse. Symptoms *can* begin as early as a couple weeks after implantation. The earliest I would guess that you might see symptoms would probably be three or four weeks after intercourse. Home pregnancy tests can usually give you an answer within a few days of your missed period.