Welcome to HCM,
Thanks for trusting Healthcaremagic and posting your query.
Continuous bleeding for 18 days is not normal.
Still there is possibility of incomplete abortion
Incomplete abortion is a drawback with oral abortion pills.
You may require D & C.
Please consult a Gynecologist for examination, diagnosis of cause and treatment.
Hope you found my response to your query informative and helpful.
If you have further concerns in this regard, you can submit those with Healthcaremagic as well.
With good wishes,