Negative blood hcg text positive urine test

Hey I was wondering if anyone has experienced this before, I recently attended a&e due to having quite bad abdominal pains the first thing they done was take a hcg blood sample which came back negative along with a urine pregnancy sample. I also took a test that day and it was negative. I have now taken a test 5 days later and it is positive ( I have taken 3 ) and all positive. I am wondering if this can happen ? And if anyone has experienced this and been pregnant ! I am just really worried as I have previously had 3 miscarriages in the past my last was in March this year. I would appreciate any advice or info you have