Adding onto that, I checked for any STIs in August and it came out negative and I have had sex with one partner since then (who is also clear of STIs). Not sure if that helps, but I want to provide as many details as I can.
You could be experiencing the discharge of tissue from an early and undetected miscarriage. Have you taken a pregnancy test? There might still be hCG in your system if this is what it was. In any case, you might want to see an ob/gyn and get an ultrasound and see if there is any unexpected tissue in your uterus. If you had been a virgin, I'd suggest this was tissue from your hymen, but you said you have had sex.
Not sure because I am not a doctor but there have been many times I had light spotting or extremely thick discharge 3-5 days before my period and it always smells different a few days before and after, I would not worry unless other symptoms occur, you miss your next period, you get other pregnancy signs or the smell worsens quite a bit keep track if this is a new monthly thing or one time thing.