I had unprotected sex & he came in me on 1/18/15. Ovulation was said to occur on 1/20/15. I'm never early on my period which is suppose to come on Tuesday (2/1/15). On Saturday 1/31/15 (12 days dpo) i started to bleed. What i thought may be my period but its not quite the same. Could this be implantation bleeding? insight please? I've read it can be mistaken for a period.