Spotting 9 days after period ended

I am 20 years old and have never had any spotting before. My husband and I use condoms so I am pretty sure it's not implantation bleeding. I am just curious as to why this would start all of the sudden. It happened 9 days after my period ended just a little bit in my underwear but when I wiped there was nothing. It hasn't happened again since. Right before it happened there was thick white discharge and quite a bit of it. It hasn't happened again just very quickly yesterday. Slight cramps and some headaches but other than that nothing out of the ordinary. Any suggestions on what this my be?