Brown spotting

Hoping someone may have gone through something similar..

I started having some light brown spotting on CD11 it got slightly darker on CD12 (I just thought it was af starting) then this morning CD13 I had a tiny bit of very light pink when I went to the toilet first thing and absolutely nothing since.

AF is due today or tomorrow. I tested today and got a bfn, I thought I saw something but there’s no colour so assuming it’s an indent.

I take my bbt and it did go down a bit today, which usually happens on the morning that af starts for me but absolutely nothing.

If anyone could share similar experiences it would be greatly appreciated!!

CD13 test