12 weeks measuring at 6weeks?

So, I should be around 12weeks by now. Last thursday(11/15) I got my first ultrasound. The tech said my sac was only measuring at 6weeks. I could have been off on the dates though. At first she said i was either having an ectopic pregnancy, or I was only 6weeks. If you go by my first missed period, its been about 6weeks.
The following Monday I had another u/s, and also had my blood drawn. My results came back yesterday, and my progesterone is at 6.5? My gestational sac was empty in this u/s, but had a speck in the first u/s. But they ruled out having an ectopic.
The doctors tell me I'm going to miscarry, but I feel like everything is ok. I have no symptoms of anything.
Has this happened to anyone else?

Yes unfortunately two of my miscarriages were missed and I had no symptoms. What were your HCG levels?

Yes and unfortunately I wound up miscarrying both times it happened to me. Sorry hon, but usually that's not a good sign

Yes
I've had a missed miscarriage where the baby stopped growing but my body didn't acknowledge the loss for 2 more weeks.

Your progesterone alone is not high enough to sustain a pregnancy. I'm sorry.

They never told me my exact hcg levels, they just said "they were low"
I have another appointment monday to get more blood drawn, and another u/s. Im hoping for the best, but im prepared for the worst.

Girl.
Im so sorry, i went through this exact last year.
Its called a blighten ovoum. I was 12 weeks but my sac stayed at 7 weeks,
no fetus. no yolk sac. No nothing.
Im sorry mama when u start bleeding thats the end of it :/
Im so sorry u have to go through this,
nothing is wrong with you. Its just something that happens
.. Im here if u wanna talk and know more k?