when does implantation bleeding occur? help please..

Piper
I started my last period October 15th, it was normal. I experienced light spotting on November 3rd and very very light on the 4th. I am supposed to start period on 14th but still no signs of it. I always have sore breast and cramps several days leading up to my period.. I've never had ovulation or "mid cycle" bleeding before..  any ideas?