Ovulation or Implantation bleeding?

Britney
Glow says my ovulation date was day 15 of my period, which I did have sex but used the pull out method.
I have been tracking my mucus for the past month to better know my ovulation date, which I tracked it to be Day 20 of my period. Well, Day 21... I had pink/brown gooey discharge. I've never had spotting between periods. Ever. It only lasted a couple of hours and was gone. I looked it up and thought it might be implantation bleeding. so, I took a test on Day 24. BFN. But, I'm worried that I might have taken the test too early??! 
My fiancé is having a lot of anxiety about the possibility of me being pregnant. So, I may take another test tonight, but is it too early to know for sure? My period is supposed to come Friday or Saturday. 
Could it just be ovulation bleeding? How long after ovulation can you get the spotting if it's not implantation bleeding?