There may be several reasons for this. First of all, it should not be ruled out that the test turned out to be defective, this happens, and quite often, especially when it comes to inexpensive test strips that are sold on almost every corner. In the desire to see two cherished stripes, some ladies go too far, starting to look for "ghost" strips on the test strips. If they find it, they automatically begin to consider their test positive, although in reality there may not be a pregnancy.
If the test still did not deceive, then the reason for the negative conclusion of the ultrasound diagnostics doctor may be that the woman turned to the doctor too early, and the fetal egg is not yet visible. The device itself may be outdated, with low sensitivity and poor resolution. The reason for the absence of signs of pregnancy on ultrasound may be late ovulation, and the presence of an inflammatory process in the uterine cavity, and, of course, the insufficient qualifications of the doctor.