Happy yet sad

Ok so we def weren’t trying but I got pregnant . I went to the doctors and my first visit they said they saw no baby just a sac barely . Fast forwarded 2 weeks later I now have what they said 2 sacs and a baby in one . The other was just empty .

Could it be possible baby was just small & not visible ? I mean the first time I went they only saw one sac and now two and one has a baby measuring almost 7 weeks ? I’m sure they could of seen that the first time ?

Help