this could also be a new pregnancy as well, he wouldnt see anything if it was as it would be too early, the only way to know for sure would be to have another blood test to see if your levels are going up or down,
Sometimes it can take more than a month for the hcg hormone to return to 0. Your doc will probably continue to test your blood until it returns to 0 or close to it (non pregnant hcg level is between 0 & .5)