Thanks for posting your query,
From your description spotting after going off pills is most likely due to pregnancy
. You could be experiencing implantation
(which could be ruled out by the fact that you are having lower abdominal tenderness/pain, as that hardly occurs with pain) or you could be having a pregnancy complication such as a miscarriage
or threatened abortion
. You will need to consult with a gynobs as soon as possible so that you could be examined and the cause determined and also eliminating other causes of spotting with missed period (especially pregnancy complications such as abortion and ectopic pregnancy.
Your situation seems to require a emergency medical care.