My last period was September 15, to September 20. I started taking birth control October 2nd, but I took October 7's about 12 hours late. I had unprotected sex on October 7, 8, 9. I started spotting yesterday, october 17. It definitely is not my period, because it's thicker and darker than usual. I've also had to urinate much more frequently. How likely is it that I have conceived? Thanks for reading.