What Causes Prolonged Dark Brown Vaginal Discharge?

OMG - dark brown discharge for 6 weeks. sometime, I have red blood for 2-3 days, then, it is dark brown thick discharge with clumps. I went to a doctor 4 times, I had an ultrasound, tests, finally biopsy...the result of this 6-week period frustrations - my doctor says that everyhting is fine. Really? Any recommendations? I am very frustrated. I am married, no sex for the last 7-week, don't take birth peels, wight is normal, active- yoga, gym, etc.