Answer:
It doesn't protect against pregnancy for future sex, but only for sex that happened in the 120 hours after you took it. With the levonorgestrel morning after pills, like Plan B, Next Choice, and Postinor, the sooner you take it, the better it works. A new option, Ella, is more effective, and its effectiveness is high throughout the fourth and fifth day after sex.
The morning after pill does not protect against pregnancy from future sex.