Do Emergency Contraceptives Cause Scanty Periods?

i had sex with my boyfrnd on 10th april though he had used a condom during intercoure, his pnis had touched my vagina when he wan't using a condom, i consumed unwanted 72 within 18hrs of having sex. my periods starts by 19th or 20th of every month. my periods started on 20th of this month but the flow is very very scanty. for example on my second day of periods i usually use 6 napkins... but this time i used only one napkin all day. am i pregnant or is scanty period a side effect of unwanted 72 medicine?