Still bleeding 4 weeks after a miscarriage

Hi I wonder if someone can help
On the 10th of July a had pain and heavy bleeding so went to a and e I had a scan which confirmed i had a miscarriage. After having a few blood test my Hgc hormone was still going up slowly so they were concerned it was ectopic. I had another scan which showed nothing. They then wanted to give me an injection which I was not happy with so everyone agreed on the expected management method and in the last couple of weeks the hormone has gone down to 66. A week ago the pains had stopped so too had the bleeding but yesterday it all started again why could this be 

Thanks in advanced 

Abby