How long does it take to get a negative pregnancy test after a miscarriage?

Hello so it’s been 20 days after my miscarriage and I still get a faint positive test. Last week my hcg levels were 47 after it was 1200. I tested two days ago and it was negative I tested today and it’s faint positive. I was 5 week pregnant but I had a blighted ovum. My doctor is going to check my hcg levels on the 20. Just waiting hormones to go back to normal. I been having sex since October 5th it’s only been a week. Any ideas ladies. How long does it take for hcg levels to go back down. I mean it’s been a week since I had 47. I thought it would be low now.