Oh glong I'm so very sorry for your loss. I had a loss at 6 weeks back in November, and the doctors monitored my hcg levels to make sure they were dropping. I bled for about a week, and then got my period at exactly 6 weeks after the day the miscarriage started. I was still getting positive tests for a long time after the bleeding started (maybe 2 weeks), so I agree you should monitor until the test goes negative.
Please take care of yourself during this time. Such a hard thing to go through. Thinking of you xoxox