Can drs blood tests be wrong?

Last month I had positive home pregnancy tests. Then I started bleeding. No clots no tissue just bleeding and no cramps. Which is so unusual for me.  And the blood test said my hcg was negative. But could they be wrong. I still have been experiencing pregnancy symptoms. Like the areolas r darker and bigger I have the bumps on them am been feeling off. I am today 5dpo some stomach pains but they leave. Just curious if anyone experienced this then was still pregnant. Thanks in advance.