Inevitable Miscarriage

A little background on what's going on with me right now...

June 16th: positive pregnancy test

July 2nd: ultrasound, no sac visible

July 3rd: HCG 24,000

July 5th: HCG 26,000. MD tells me since HCG did not double pregnancy is considered non-viable and to expect to miscarry in the next couple of weeks

July 17th: second ultrasound, still no visible sac

July 29th: HCG 70,000

August 1st: 3rd ultrasound, still nothing visible

As of now MD seems perplexed. He expected HCG to lower and for miscarriage to have started by now. The pregnancy is classified as "inevitable miscarriage". I have had no bleeding, no pain, no discharge. So far the 3 ultrasound's have been performed by MD on a mobile device but all have been vaginal. He wants me to have a vaginal ultrasound with the ultrasound technician with more advanced technology to make sure nothing has been missed and pregnancy is not ectopic. I'm so confused as to what is going on. Has anyone experienced anything similar or know anyone who has?