Late Implantation?

I’m driving myself mad!

I had peak ovulation day 17 of my cycle, not long after I started noticing symptoms - although pretty sure I just imagined them! I took test 9dpo and 10dpo and both BFN. Then 11dpo a very small amount of brown discharge started and today even more but it’s really dark brown and only when I wipe. I’ve never had this before AF. Due AF tomorrow. Is this normal?!? Would this be implantation bleeding? Currently I only have a 13 day luteal phase.. I should add I feel very unwell today - crazy headache!