Bleeding first day of fertile window?

Okay so, let me start off by saying I've never had this happen before. Well today I was sitting down and thought I was just having discharge, so I went to the bathroom to clean up, and it turned out there was a bit of blood (not a normal spotting amount, but not enough to be a period), and now I'm having a darker brown discharge.

I'm kind of freaking out because I realized I've been having mood swings, back pains, and headaches for the past few days.

Any clue on if this is just normal or?