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The spotting could be due to pregnancy, birth control pill use, infection etc. If you have been taking the birth control pills regularly without missing them in between then you are safe. If you have missed taking the pills, then you are at risk of pregnancy.
The spotting, also known as breakthrough bleeding is also a common side effect of birth control pill use. Visit your gynecologist for a thorough examination and tests to confirm/rule out chances of pregnancy. Discuss about alternate birth control use to minimize the side effects.
Take care.