Hi...when My Pregnancy Is 9 Weeks Old, It Was Revealed

Hi...when my pregnancy is 9 weeks old, it was revealed in the scanning that baby died at 6 weeks only. So doc gave me medical abortion kit. Bleeding started on that day. Now it's third day and iam getting pain on the left lower abdomen.she gave me meftal spas injection and I am still getting pain on left side. Iam very scared. May I know why? Doc said that if all pieces dint come out she would then do an d and c.