9 days late and got my period

I last had my period December 1...when I didn't get my period on the first of jan I started thinking maybe I am pregnant my cycles are 28 days .But when i tested on January 8 got a negative 😫On Saturday I started lightly spotting today It's heavier but I am getting this left pain that comes and goes by the ovarie .I read a lot online I doubt it's implantion bleeding 😖😤I am sad it's been a year of trying really thought I was pregnant how did my cycle Go from 28 days to 40