help ?

irina
Last month i took the pill , plan B or smth like that  on 2.09. and my menstruation normall comes on 3.09 but it comes on 7.09. . This month my period should comes on 9. 10 but it passed 4 days and nothing  .. it's just a dereglation or it's about a pregnancy ..? it never passed more than 3 days ..