Positive after mc hcg not lowered or new pregnancy?

I lost my baby I was about 9-10 weeks on the 27th of July (the mc started and I passed baby on 30th) I went to hospital last Tuesday as they told me to test then and they're test came back negative although I had a very faint line that morning, I had tested every day for 4 days prior and they were getting fainter.. I took a test today as advised to again and it's faint positive again.. is this a new pregnancy or can the hcg stay in my system this long? I have sore boobs, nausea and lots of white cm also 5 days late for af, please help x