6 weeks and no baby on ultrasound

I had an ultrasound today and by the calculation of my last period I should be 6 weeks and 2 days but there was no baby on ultrasound and I had a transvaginal. I haven't had any spotting or bleeding. I have taken several home pregnancy test and they all were positive. I had blood levels drawn today, but I was so sad not to see a baby. Has this happened to anybody else?