Cd 51 ; BFN; observed tiny brown spotting

My last AF was March 14 th 2018. Now today when I went to restroom I observed a tiny brown spotting .

If I had got my periods on April 16 th then my fertile days are April 28 th to May 5 th .

So since I got this brown spotting today am I ovulation soon ?? Or is this a sign my AF will start ?

So confused .... need inputs!!

Thanks in advance.