What Causes Bleeding And Abdominal Pain After Taking I Pill?

hi, i'm 25 year old girl.. i had my last period on 24th may and i had sex on 31st may.. i took i-pill on the same day we had sex ... and five days after taking the ill, i'm having vaginal bleeding with abdominal pain , and the bleeding is more likely as my normal period but a little less.. is that normal?? when will it stop? i started bleeding last night.. plz help...