six weeks and only a yolk sac

Dusty
Has anyone had an US at six weeks and there was only a yolk sack but no baby?  They're telling me this pregnancy may be ectopic but there's no way to really tell yet. I have to go in every other day to have my HGC levels checked and I have another sonogram on Monday. My OBGYN did my sonogram not a tech. 
Edit: they fear I may have an ectopic pregnancy.