late implanter

so, today, according to glow, i would be 5 days late. thursday, I had very very very light, kinda hard to see, brown spotting. Not enough for a pad at all. yesterday, same thing. this morning, I didn't have any at all. I cramped so bad on Thursday and then the spotting occurred. Has anyone ever heard of or had a late implanter? I have no clue when I ovulated, so that doesn't help any. FYI, when my period is due, I start on the exact day and it's a super bright, red, heavy flow.