Help. No gestational sac at 7 weeks. Did I definitely miscarry?

This was after an FET so I can't imagine the dates being wrong. My Hcg was over 3000 at 4-5 weeks. The doctor says it's possible it might be too early or that she missed it with the vaginal ultrasound, but I think she was just trying to be positive.

What is giving me (some, maybe crazy) hope is that even though I've had no nausea, I'm still getting crazy thirsty. And I remember that everytime I've had some kind of ultrasound done, someone always comments that my uterus is weirdly positioned. I can't remember the words used but maybe something like 'compacted'.

Just wondering if anyone has any stories where the doctor might have missed a gestational sac? I know it's probably a miscarriage, but still wondering...