Baby's growth is lagging behind.

I need to get this off my chest and hope this is the right place to talk about it.

According to my own calculations, I'm currently 8 weeks pregnant with our second baby. I'm not entirely sure because my cycles varied between 29 and 31 days. However, I had a super faint test on August 7th and on August 12nd it was a clear positive, and the Clearblue indicated 1-2 weeks, so it should be around 8 weeks.

We had the ultrasound yesterday and the results are probably not good... The midwife saw that my uterus was about the size of 8 weeks and was completely intact, but the gestational sac only measured 5/6 weeks (on the screen it said 5 weeks 3 days). It was so small that no heartbeat was visible. We were sent home with the instruction to come back next Tuesday to see if it has grown or if it simply stopped growing at 5/6 weeks, but we are told to assume the latter.

I'm quite sad about this and my feelings are so contradictory because I feel so pregnant and don't feel like anything is wrong, even though the ultrasound didn't look good for this stage..