is only possible, if unprotected sexual intercourse is done around ovulation time in regular cycle with ejaculation.
In your case,you did sex 3 wk after last abortion
without ejaculation.So chance of pregnancy is almost nil (pre prostatic fluid/pre cum,released before actual ejaculation, has slight chance).
You also not take those pills completely.Do a USG pelvis to rule out underlying pathology if any and confirm whether it is abortion bleeding or withdrawal bleeding of the pills,more likely period.
Consult with your gynecologist and take advice accordingly.
Practice safe sex
in future and use pills completely on scheduled time to avoid unnecessary vaginal bleeding.