Vanished embryo

I went yesterday for my first checkup (7 weeks) after my ivf implantation, and the Dr couldn't see anything. I was asked to take a hcg blood/pregnancy test to see what's going on. Meanwhile, mind you, I've haven't had any symptoms of anything.

The results came back in the evening that no. I wasn't pregnant anymore. It's just bizarre, as I had no miscarriage symptoms, bleeding, spotting, nothing. The embryo just "disappeared"! Have any of you read or head of something like this before? I'm just baffled.