Had unprote sex on 18 mar & took ella (ulipristal acetate) on 19 mar. previous period started 24 feb and end 7 march. neg pregnancy test, late period, any chances of preg?

Small chance: Irregular bleeding after taking a morning-after pill, like Plan B or Ella, (ulipristal acetate) is somewhat common. Some women get spotting or bleeding before the next period. Women may also have a heavier or lighter next period, or a period that is early or late. A pregnancy test can be done 3 weeks after taking a morning-after pill, to be sure the pill worked. A negative result means no pregnancy from 2-3 weeks ago.