Why is 90 percent of my period stringy black brown blood. if not all of it (which is what happens most of the time) it doesn't feel normal.

Hormone imbalance?: The abnormal flow and consistency of your menstrual blood suggests that you aren't completely shedding the menstrual lining during your period. Normal menstrual cycles require a very orchestrated interplay of reproductive hormones. If there's an imbalance of these hormones, menstrual irregularities and abnormalities can occur. Please see your gynecologist about this.