Hcg level

Hi everyone! On July 31 I tested positive on 4 clear blue digital tests. Today, August 11 I went to the doctor for my first appt. And my urine(4th time going for the day) was negative for them, And my blood level was 20hcg. They are going to recheck on Thursday 48 hours later... And right after leaving the office I picked up 4 more and all stated positive. Looking on the instructions it says clear blue picks up 25+ level of hcg. Help!!! Has this happened to anyone else!?