urine test positive, blood test negative??

I had a miscarriage last month on February 14th. My doctor said to wait 1 cycle before trying again. Needless to say, we continued to have unprotected sex after the miscarriage in hopes of getting pregnant. I took a pregnancy l test 4 weeks after the miscarriage which came back negative. And another test 4 days after that which also came back negative. A week later I still hadn't gotten my period and decided to test again. I got a faint positive. The doctor sent me for a blood test which came back at only 5. They are telling me its just left over from my miscarriage. However, my tests are continuing to get darker and if it were left over from the miscarriage why did I get 2 negative tests in between. I'm also having pregnancy symptoms (sore boobs, nausea, and crazy mood swings). Anyone else have a urine test come back positive and blood test negative and end up having a healthy pregnancy?