Yaz and forever bleeding

I was put on Yaz almost 4 months ago for possible endometriosis. It worked like a charm within the first month and I was having no periods along with very little pain. My dr wants me to not have a period at all so I take the pills continuously. A little over a month ago I had break through bleeding and it hasn't gone away. The bleeding varies between moderate to little flow. My dr didn't seem to concerned with it but I have a history of anemia and am concerned. Anyone else have problems like this with Yaz?