What could this be?

I’ve been experiencing mild cramps/bloating and brown discharge since cycle day 16. It started off with light pink spotting and then turned brown with a few blood streaks in it. I’m on cycle day 18 now and it’s just brown but it’s there every time I wipe. I’ve been using OPKS this month so I’m pretty sure I haven’t ovulated yet so I’m almost positive it’s not implantation bleeding since implantation happens between 8-12 dpo. Could there be any other explanation as to why I’m experiencing this?