Pregnant after miscarriage?

My fiancé and I suffered a miscarriage on Aug. 6th. My doctor said that my quants were down to 1 two weeks ago and that we could start birth control soon. I decided to wait to start my birth control until the end of my first cycle. I started having weird dreams again and craving fruit so I decided to take a pregnancy test to give me some answers and it was positive! Could it be that I still have hcg in my system from my miscarriage or could I really be pregnant again so soon?