Unsure after Drs

So I went for an ultrasound 2 days ago for PCOS where the guy doing an ultrasound stopped and asked if I had done a pregnancy test. I said no I'm only 18/21 days. Which he responded with um ok could be a bit early anyway. I had an urgent call from dr tonight saying they needed to see me urgently. They found a mass on my uterus which appears to look like early pregnancy. I don't want to get excited as AF is due today Which she hasn't arrived yet only slight brown discharge. Has anyone else experienced something similar? Thanks ladies x