When To Take The Pregnancy Test For Accuracy?

Hi. I've had this coconut like substance once, during contact with my partner. It just happened once. I went to see my OB, she took a Liqui-Prep. The result says, Benign smears with severe inflammation and reparative changes Bacterial Vaginosis. What does it mean? I am also assuming that I am conceiving, I am 3 weeks delayed right now, I took a pregnancy test a week ago and it was negative. My OB prescribed me Duphaston. Today is my 2nd day after my 5day Duphaston intake. When should I take a pregnancy test? Is it accurate if I take a test now?