misdiagnosed miscarriage? I'd love to hear your story!

I had a scan at 6w & 7w both showed sack with a yolk sack docs said it didn't look viable and to expect miscarriage within a few weeks... my hcg was still riding at 8 weeks.. well that was a month ago.. I've been waiting 4 long weeks and nothing has happened. My stomach is growing & my breasts are still growing and extremely sensitive. I've miscarried before and all my symptoms went away so I'm just not convinced yet. We've decided to have another ultrasound in a few days I'll be 11w2d..I'm so nervous but hopeful.. anyone else experience something similar?!