Went to get ultrasound and saw nothing😢😭

I went to get an ultrasound today supposedly calculating from my last period on May 6 I should of been 6 wks and 6 days. I went in for a vaginal ultrasound and saw nothing, they can see the gestational sac. So they either came up with the conclusion of either I ovulated on a later day and I am less weeks maybe 3 weeks pregnant or I have to be prepared myself to a ectopic pregnancy. I wonder if this has happend to anyone? I suffered a stillbirth in March 2012 so this is my rainbow baby i dont know what to expect it just feel so down, depressed. After 4 yrs God send me a BFP and look at what's happening. They gave me another appointment for 2 weeks to see if it just was I was early and I'm 3 wks preggo or it didn't form.