Pink,
I can relate to your woes. Very familiar to me. Firstly yes, doctors will want to rule out dating of fetus from LMP. That's because not everyone has 28-days cycle. I have 37-days cycle so if by LMP mine said 7 weeks, i usually have to minus like 10 days. So I get my own reliable EDD based on my own guestimation. Anyone can have short or long cycle at anytime of the year. Dating pregnancies are most accurate by scanning. If baby is not seen but sac is seen, then date is calculated by sac size. Usually 4-5 weeks, u can see sac. If you can see sac and yolk sac, it's usually around 5 weeks. 6 weeks onwards, you should be able to see a bigger, rounder sac, a yolk sac and fetal pole. Actually fetal pole IS the fetus. So i'm quite confused when u said no fetus. By 6-7 weeks, heartbeat should be detected and CRL is usually around 3.3mm-5mm. So if your measurement is around those region, u can guess how far along you are. Based on your CRL size, you could be just starting 6 weeks. 2mm is too small to see heartbeat. Need at least 3.5mm to be able to see well, then again it depends on how sensitive your gynae's machine is.
By repeating blood test in 48 hours, they will monitor if your HCG hormone doubles. If not doubling, sorry bad news. If doubling, still got hope. You can wait for a few more days for repeat scan. No use going for 2nd opinion on the same day.
Is you gestational sac nice and rounded or is it looking irregularly shaped? B'cos if former, you're doing good. Are you having any pregnancy symptoms? If so, still looking good too. Staining is quite common after scan b'cos your cervix is irritated by the tool. I get staining now and then on my 1st pregnancy too.
I think you shouldn't get traumatized yet. Let's wait for a week and update us with anything. From the bottom of my heart, I wish you good luck. Rest well yeah. Take MC and stay in bed.