empty sac

Ok so I need some help. I have had two back to back miscarriages, chemicals whatever . first was in April the second started May 25. I got a BfP on July 1 . had labwork done on July 3 and 5th hcgs were 95 then 310. doctors office didnt want to do any more labwork. my first appointment is August 15. we couldn't wait for an ultrasound and i thought i would calm my fears and went to ultrasound place today. they only found an empty sac :( measured 1.9 cm. I am devastated .they said to call my doctor and see what they want to do. anyone have any experiences with this ? I figured I would be 7 weeks since I have had 3 weeks of positives. maybe I'm earlier than what I thought ? I honestly have no lmp to go off of due to the miscarriages. please let me know you're experienced. I am trying to be positive but prepared for the worst.