Is Bleeding After Taking I-pill Normal?

i had a sex at 3rd of feb 2014,i took i-pill after 18 hours,my period is supposed to start on 27 of feb,but bleeding started after 8th day,is it compulsary to bleed after taking i-pill? We again have a sex on 27 of feb .e on probable day of normal period.again i used the i-pill.how much i m secure from pregnancy?when should i expext my periods?