Hello everyone. There was a two-week delay in July, I had an ultrasoun…

Hello everyone. There was a two-week delay in July, I had an ultrasound, they said I should call for Dufaston. My period started. The cycle turned out to be 45 days. In August there was another delay, the test is negative. I'm waiting still. I repeat the test and it's negative. I take Dufaston for 5 days, why do I need to repeat the test and it's positive? Can Dufaston cause a false positive?