I am not a doctor but I have a story to share. My best friend was on BC for years. She was on an antibiotic and her birth control was less effective. She continued to take it anyway. She had a headache that lasted for two weeks. The doctor told her it could be the change in her hormone levels, however, two months later she found out she was 8 weeks pregnant. Not for sure if this helps.
I think you are protected for a few days after stopping birth control pills.