Thank you all for your comments.
Im just thinking if it could be a quemical pregnancy even if I had the last Pregnyl shot 1500 iu 10 days before...
This will be a very loooong weekend waiting for Monday to go for a blood test. Still no signs of AF and my boobs are very sore, more than the past days.
I don't really think there is a lab mistake, but I wish it was only that.
A vanishing twin? Can that be possible if they only transferred 1 embryo? I mean at the stage the embryo was, is it possible it could split?

Juniper, that sounds great! Good luck for Monday!
Beestrong, I am sorry that the embryo didn't make it to transfer
Beau, I was told the same than Jasmine00, that cramping can be just the uterus stretching.
Jasmine00 I don't really understand how embryos progress, and perhaps they just needed a few hours more to get to 4 cell stage? Lucky you have 7!
JoeSpratt good luck with DHEA!
Kel82 Im glad to hear your operation went well. Look after yourself