Light brown blood?

My cycle isn’t regular yet, but I was guessing AF would come tomorrow bc I’m 13 DPO and woke up this morning to what seemed like a brown period, but when I wiped it was really light brown and kind of mucousy like discharge. It’s heavier than spotting, just like a light period, but I usually start off with my flow a little heavier than this and it’s, of course, usually red. We did try on my fertile days this cycle, but I took a test yesterday and it was negative. I also had a CP at 5 weeks at the end of December. Any thoughts?