False positive or too early to detect???

Erica • Married with two beautiful boys. Trying to loose the weight and not get prego at this time.
So I have had positve tests from the $ store and frer tests for 4 days now. I needed a pregnancy confirmation so that way my insurance will kick into gear. Emergency rooms test were negative! How is that possible? Aren't their tests just as sensitive as the $stores??? The dr knew nothing about really being pregnant at all. Asked questions and he said idk!