Dark brown/reddish discharge?

Hi ladies! So today as I was changing I noticed that there was a dark brown spot in my panties today. I'm in my second day of my fertile window. I've had brown discharge before, but to be honest I don't know if it's more noticeable this time since they were white panties. I had sex a month ago but we used a condom that didn't break. Is this normal or should I be concerned? Thank you!