Hi willing, I'm so sorry to hear you are going through this. I would definitely go back and ask for another scan to see what's happening. You've done amazingly to wait so long. I started to miscarry on 5 Sep and wanted to let it happen naturally but after 2 and half weeks of bleeding I broke down and phoned asking for the surgery. They gave me an appointment for the following day but I actually then passed the sac on the next morning so by the time they scanned me again everything had gone. I bled lightly for another 7 days after that.
They did do a scan midway through my two and a half weeks of bleeding and told me the sac had shrunk right down and it looked like my body was eeabsorbing the pregnancy. This may be the same for you and hence the long time. But do get it checked out x