You probably should have taken pills for several days after sex, because sperm can live in the body for up to a week. You could have ovulated a few days after you stopped the pill and become pregnant.
HOWEVER, I feel that's very unlikely. You'll know in two weeks, huh? You can test two weeks after you had sex, and the test will be accurate. Also, your period may or may not come as a result of stopping the pills like this, so you really can't depend on that.