What Causes Brown Vaginal Discharge And Frequent Urination?

I am 32 years old, 5 foot 4 inches, I had a hysterectomy 2.5 years ago. I had PID and endometriosis. For the past month I've had a brown discharge, abdominal pain,no appetite, dry heaving, frequent urination. I went to my family Dr. 3 days ago. He diagnosed me with a pelvic infection. I have a ultrasound in 2 weeks, had blood work done and was put on 2 antibiotics. I still feel terrible. What are the chances of this being some type of cancer?

P.S . I have one ovary left everything else is gone