The very same thing happened to me, at 3 mths just after we told people. it turned out to be a non neclis pregancy basicly there was a sack a cord and a placenta but no baby.
the midwife told me 'not to be sad a nature was doing her job, and if i thought about, when nature mixes a million genes together to make a baby something will go wrong somtimes,
I started to miscarry on the saturday and i was getting married on the tuesday.
I was gutted
but then i got pregant the very next month, and now we have have Fin who is 14 months old.
so dont be sad. Though you wont be able to help it.
and please belive me when i say it is nothing you have done, it just nature