6 1/2 weeks ultra sound Only sac

I track My periods after I received depo vera and I believed I was 6 1/2 weeks. Well I started bleeding dark red blood so I went to get an ultrasound to find out They believe in not 6 1/2 but 5 weeks. They said They see the gestational sac but No baby. and They are goinf to check My blood levels. anyone else happen to and What was ur results