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If this discharge is not correlated with menstruation
and last for many days , then you need properly assessment , most valuable in your case transvaginal ultrasonography
( can examine your vagina, cervix
, uterine cavity
), pap smear
, urine analysis, microscopic exam of your discharge and culture( to rule out any bacterial infection). Dark brown, chocolate discharge are signs of blood and you need find out cause and accordingly will be more easy choose treatment.
I wish you good luck and speedy recovery,
Hope this helps and I have answered your query. If you have additional queries don’t hesitate to ask.