Spotting

My last period was 24-30th November and my ovulation date isn’t estimated until around the 16th December. I had sex on the 3rd December and am now having some slight cramping (very minor) and some light spotting (only on panties, not when I wipe). Does anyone know why this might be? I hadn’t had sex for a few months prior to this recent time so I’m wondering if it’s from friction or something like that but that wouldn’t explain the ‘cramping’.

It’s obviously not pregnancy/ovulation related. Any insight? 😕