How fast can implantation begin after having sex? The reason for my question is that 29 hours after unprotected sex I took plan B. Two weeks later a pregnancy test showed pregnant. Plan B can be used to stop pregnancy up to 72 hours? Im so confused!

Plan B doesn't always work, it's not 100% effective, looks like it didn't work for you.

The only form of birth control that works is abstinence. Plan B is only a PLAN not a guarantee.