Hi, and thanks for your medical question on eHealth forum!
The pain in low back and lower abdomen pains can be due to pelvic inflammatory disease or due to vaginal infection as these are common side effects of abortion. If you do not get periods until Jan 18, take a pregnancy test. In Dec the periods got delayed due to the medication you took. If you keep getting delayed periods and do not conceive then consult your gynecologist regarding this. Hope this helps. Take care!