What’s the latest you’ve received a false negative?

G

I’m 14dpo expecting AF today and am having a very weird experience, mild cramping and a bit of brown spotting which is not normal for me at all (my periods usually start very heavy). I took a pregnancy test and it looks pretty negative. Is it possible it’s a false negative, or by this point in my cycle should I be expecting a BFP if I were actually pregnant?? Do I buy another test or just accept that this isn’t our month?