Yea that happened to me, then it didn't turn out positive at the docs until I was 6 weeks
When I was about a week over due I had some pain and went to the hospit al and had a urine test. The urine was negative but the doctor decided to check for any std because the pain. When she checked my cervix was blue and immediately ordered a blood test which came back positive. Does happen. It depends on how far along you are. I was 4 Weeks pregnant. Very early.