is it implantation bleeding or is it my period because of plan b

Hi,

I took plan b emergency contraceptive 15 days ago around may 18th while i was ovulating. i have seemed to have gotten my period on time on the 1st. but i don't know if it could be period or implantation ?
my first day it was a normal flow in a red color like a normal period, its been 4 days i have had the period, but the 3rd day i got like little clots and one medium one. since i got what seems to be the period when i make efforts like to stand up or move i get little flows like in my regular period.

My usual period lasts about 6-7 days with a heavy flow. but i have only 4 days and its still a normal flow, because i have had to wear a pad everyday.

Is it implantation or a period? I'm asking because for some women its different.