What Are The Side Effects Of Using Emergency Contraceptive Pills?

good morning I am 22 years old.I had sex on the 4th of may and consumed an ipill after an hour s time. untill now,i.e,the 15th of may i havent experience vaginal bleeding. The next due date of my periods is on the 19th of may. Also i took up a home pregnancy test on the 14th of may with the results negative..Is it necessary to have vaginal bleeding?please guide me through and is there a risk of pregnancy?