What Causes An Abnormal Period After Taking 'morning After Pill'?

basically , i had sexual intercourse on the day i finished my period , i took the morning after pill the next morning and i came on my full period 4 and a half days later. I told my mother that i had 'randomly' come on again ( as she doesn't know i took the pill ) , so she asked the doctor if it was normal , and he said it is rather unusual , so she has booked an appointment for tommorow. i have now come off my period , does this mean the doctor won't be able to tell if i've taken the pill or not ? because i really don't want my mother to find out . please send me replies ASAP ( TONIGHT ! )