Miscarriage & Pregnancy Please Help.

I miscarried 5 weeks ago. On April 23 my doctor confirmed my hcg was at 120. Down from the 360-380 range in 48 hours. She didn't monitor it back to 5 though or a non pregnant range. Now it's been 5 weeks since the bleeding stopped and I still don't have a period. I was told to take a test at the end of May if I still hadn't received it. I got a strong positive.
 Here's the events:
April 23-miscarriage confirmed hcg at 120
May 23- positive pregnancy test.
Is it possible it's left over from my miscarriage or is this a new pregnancy? Could it take 5 weeks for a level of 120 to go below 25? Please help!!!!