What Causes Skipped Periods After Taking Morning-after-pill?

i'm a female 26 years old,i took the morning after pill,and a couple of weeks later i had bleeding dat lasted for 4days,its been two months and i have not seen my period,i have been having cramps in my tummy for 5days now,and i still have not seen my period,i would like to know if the drug altered my system of if i am pregnant,thank you