Completely disheartened yet trying to stay positive for our little rainbow 😔

Keels.
I went into premature labour at 17weeks with our identical twin sons in April this year, after I'd delivered our second son I had haemorrhaging & lost 3 litres of blood, requiring emergency surgery and was given a D&C in the same operation. 
We started TTC as soon as my post op bleeding ceased, 10 days later. I've never been so OCD as I have been since then taking my prenatals and ensuring I'm as healthy as I can possibly be.
I'm 99% certain of the dates in which I ovulated and am 100% certain of my last period, with these dates in consideration and 3 positive home tests and two positive blood tests confirming pregnancy that I should be 7 weeks exactly today with our little rainbow 🌈. Out of fear and worry, I told my Midwife that I wasn't sure of my dates and wasn't sure how pregnant I am. 
Today we went for our first ultrasound in order to date pregnancy & to ease my mind for the moment. However, our technician quickly pointed out the sac but took a while to find a slow flickering which she then identified as our baby - measuring 5weeks 5days - my heart sank 😔 if anything this scan did the complete opposite of what I'd hoped it would. She has recommended a rescan to assess viability due to slow fetal heartbeat
Could anyone offer me any advice from personal experience? Could this get better? 
💙