I have a weird situation and need advise:

11/20: Period Starts
11/24: Period Ends
11/24: Start Birth Control (Take two pills)
11/25: Stop Birth control
11/30: Period Starts (Too heavy to be spotting)
12/01: Negative Pregnancy Test
12/02: Ovulation (According to ovulation calculator)
12/04: Period Ends

I'm wondering why I had a second period during November, this had never happened before, was it maybe because I took two birth control pills? What's the possibility of pregnancy, I have had unprotected sex throughout the month.

Thank you!
:-D