CD45 backache and spotting

Donald • TTC baby #1. Off BC since July 2014. Cycle irregular

The other half has been complaining for a couple of days that her back aches and it comes and goes, then on CD 45 she had light spotting.

She come off the pill in June/July and has only had one sort of period since then, so we are not sure what's happening. The funny thing is we BD just a week ago so in my mind I'm thinking she's having implantation bleeding.

Are we hoping for a lost cause?