What Causes Menstruation In The Mid Of The Cycle After Taking Morning After Pill?

My last period was from the 24th to the 31st Feb; I then had intercourse with my boyfriend on the 2nd of March, during which the condom split. I am currently not on the pill and therefore took the morning after pill on the morning of the 3rd of March. I now seem to be on my period again; it started on the 8th of March. Is this normal? Will my cycle return to normal? Does this mean I'm not pregnant? Thank you