Kitty, miscarriages are never anything you have done, so please don't worry yourself.
The egg may not have implanted properly, or it may not have been viable at all, say there were problems with the sperm meeting the egg and cell division isn't happening the way it was meant to, etc.
If you are having negative tests, you are no longer pregnant. Sorry :(
Basically the tests pick up hGC which if no longer produced means you are no longer pregnant.
I doubt there is anything wrong with you. Not all pregnancies are right and able to develop properly. Unless you have had several miscarriages, at which point your doctor may start getting some tests done.
Around 25-50% of pregnancies end in miscarriages. A very large number of those are chemical, ie they never implant properly and are lost very very early. Then the number decreases little by little on your way through the 1st trimester.
Please look after yourself and once you are ready, try again. Good luck for the next one.
I hope this helps.