Had sex 11 days after period, took plan b right after. had bleeding a week later (day 18), is that my period or will my period be late now?

About Plan B...: Plan B can alter the menstrual vaginal bleeding for the cycle in which Plan B was taken, and sometimes the next cycle too. One should be sure to check a home pregnancy test about 3 weeks after sex, because Plan B works most of the time, but not all the time. If vaginal bleeding symptoms become very worrisome, a visit to one's Ob-Gyn or primary care doctor may be needed.