How long will Avastin keep ovarian cancer at bay?

I have Stage 4 cancer and I’m very unhappy with my oncologist. I live in a rural area and he’s my only choice unless I travel out of my community. I’ve been on Avastin only since last August. Chemo probably got rid of a lot of small tumors in my abdominal area but not some larger ones. In my last visit, my oncologist just said how lucky I am. Avastin usually only works for 6 months. He is really, really bad about answering questions and I think about giving adequate information. Does anyone have better information on this and what to expect?