Hii ,
Welcome To HCM & Thanks For Asking Your Query Here
As you mentioned the discharge is blackish and Black
vaginal discharge must always alarm you. Dark discharge can be caused by hormonal therapy, ovulation, implantation, inflammations or STDs, after sex and vaginal traumas, after Defloration and it should be thoroughly investigated
However Normal menstrual bleeding usually last 3-7 days and You are bleeding constantly for 11 days which should not be ignored
This prolong bleeding (Menorrhagia) is most commonly caused by hormonal imbalance as Changes in your body's level of the hormones estrogen and
progesterone can disrupt the normal pattern of your period
however there are variety of other medical conditions which may causes this including -
Polycystic ovary Syndrome (PCOS) , Overactive thyroid or
hyperthyroidism ,Thickening of or polyps on the uterine lining ,
Uterine Fibroid etc and it needs thorough medical check up and investigations to spot a confirm diagnosis
I would strongly suggest you to visit your gynecologist ,He/She will examine you thoroughly and may go for an Ultra sound,few blood test for Thyroid Function and hormones imbalance and all other necessary medical investigations to rule out underlying medical condition
I hope it help
Thanks & Get well Soon