delayed period or pregnant?

i am a first timer user of combined pills i had it last march 18 because i have a unprotected sex on march 17 im on placebo pills now but i dont have period...i have lots of tracker tells that i should have a period on april 6 or 7 but its already april 9..is it normal or should i start worry that im pregnant..?and whats the causes why i had a delayed period?someone can explain to me and clear up my mind ....im so stress thinking of this...thank you in advance...