I miscarried at 12 weeks, my dr said the baby had probably not made it past 5-6 weeks. There had never been a fetal heart rate that could be detected, and my nausea was only a day or two in the 4th-5th week. A blood pregnancy test confirmed I was no longer pregnant.
Typically you can't find a fetal heart rate until close to 12 weeks. Trying to find one at 8 weeks, and not finding it, doesn't mean it's not there, it's maybe too tiny to be detected. If you still have pregnancy symptoms, I'm not sure I'd say you've miscarried. You may want to take a wait & see approach?
One of my girlfriends was almost 15 weeks pregnant before a heart rate was detected, because her uterus actually had a fold in it, and the baby was behind the fold. Once the baby started to grow, the uterus stretched out the right way, and everything was fine. Her dr had told her the same thing, and when she didn't miscarry for weeks, she was worried she'd need a dnc....she saw a different dr, and there was her baby girl, perfectly healthy...and alive....all along.
Maybe just give yourself some time. If you still have symptoms, that could truly be a good sign. If there is no change at the 12 week stage, then maybe you should have an ultrasound to take a good look. I hope I'm not steering you wrong, but that was my experience, and a friends'.
Good luck! And I hope everything turns out well. If not, then I'm so sorry, as I do know how it feels to miscarry.
S.