Confused

At 7 weeks I had an early ultrasound at a stand alone place and it showed a baby with a yolk sac and its heartbeat was 144. At my Drs appt for my 10 week "first" appointment the Dr said all he sees is an empty sac. He did a transvaginal and was unable to see anything, the sac or anything so he did an abdominal ultrasound and he said that he wasn't able to see anything inside of the sac and he doesn't think a baby formed. --- but a few weeks ago I saw a baby! And heard the heartbeat. How is this possible? He sent me for repeat labs friday and again this monday and he will do another ultrasound on thursday. Has anyone else had this happen? What was the outcome?