Black blood. Cervical is healthy. thnx!

Hello respected Doctors. Greetings for the day. I am 36 yrs old unmarried virgin female. Weight 45 kgs n height 5.3. Last year I had one each functional cyst in both the ovaries. One was a hemorrhagic cyst on the left ovary and other clear simple cyst on right ovary. They were tiny. I was bleeding little by little in the month of May which forced me to go to the Doctor. She didn't prescribe any medicines and after three months I did usg the cysts were not there. My periods and all are normal. But this month my period cycle is 21 days. Last month was on the 28th Jan. This month it started on 20th Feb. Now the problem is I am getting the brown black discharge. No red blood I see. My date was supposed to be on 28th Feb. How come this black n brown blood. Its not coming in the flow. I don't have any diabetes or thyroid. My HB is 11.9 .. KFT normal. I am also suffering from mild viral fever coz of whether change. Kindly advise about this brown black blood. My cervical is healthy. Thnx