Hey, I am just curious as to what causes this and the meaning to it. But during my period which is very bipolar due to the fact I ve had cyst before on one of my overis but has disappeared, as far as I know. Well, my period was very painful in the beginning and bleed alot the first day second day wasn t so bad it was a lot lighter. But on my third day my blood was very dark brown and I had a black stringy thick discharge, and I did have unprotected sex the night before. And on the last day I spotted brown blood. What caused the black stringy discharge, my cyst issues, unprotected sex, or pregnancy? How you can help answer my question.