You know what, as a doctor, I have to say your doctor sucks. Yes, the oregon health plan makes it expensive for physicians to run tests, byt we didn't get into medicine to make money, or we would be in banking or something like that.
We are there to help people, and if you are distressed and worried about whether you are pregnant, then it is your doctor's responsibility to help assuring you that you either are or are not pregnant.
To try to pass that responsibility off on a commercial, over-the-counter test is irresponsible, imo.
So go back to your doctor, or insist to the nurse that you get the test. Unless that doctor made that otc test, he/she can not guarantee that it is accurate.
You can tell them (and it would be true), that if the test turns out to be faulkty and you are pregnant, but per your doctor's order act as if you are not, then any potential harm to the pregnancy or birth defect outcome is a lawsuit directly at that doctor.
And your doctor should know this.
Now, did you actually get hold of your doctor before, or only the nurse? Insist that the doctor calls you back, don't accept a brushoff by the nurse, she is not a physician and does not know the reliability of the otc test versus a blood test.
So for your peace of mind, start badgering your doctor's office until they give you some kind of reassurance, preferrably through a blood test.