What Causes Delay In Periods After Taking Ella Plan B Pill?

i was with my boyfriend for a night and we got a little carried away. he put his penis in my vagina for about two seconds and then took it right out this happened on the 20th (6 days before i was scheduled to ovulate) then on the 27th ( a day after i was scheduled to ovulate) his penis was put in again but only for a few seconds. About 5 days later on the 1st of August i took the Ella plan B pill. i know it is supposed to make your period late but it has been four days and i havent gotten my period yet. Is there a possibility that i may be pregnant? thank you