Plan B can indeed mess up your menstrual cycle, and yes, it can bring on what seems like a complete extra period, sometimes about two weeks after your real one. Different women respond to it differently.
The June 5 period was probably in response to the May 5 Plan B; and the fact that it was a full period would mean that you weren't pregnant at that time.
And the fact that you took Plan B on June 6 means that in all likelihood you'll be irregular for another month or six weeks, OK? Be super careful about birth control during this time, especially until you settle into a regular cycle again. (That might be in August, depending on how your body reacts to this month's dose.)
Does that help some?