Spotting during fertile window

I am currently in my predicted fertile window and should ovulate in 2-3 days time (I’m tracking with OPKs) but the past couple of days I have had some spotting similar to the picture.

It has only been once per day and only when I have been to the toilet and wiped, no need for pads etc. I have also had a little bit of lower back ache.

This doesn’t happen every month but has happened around this time of the month previously.. I’m just concerned as we are 2 years in ttc baby number 2 and I’m concerned there’s something wrong.

Has any experienced similar?