No gestational sac on ultrasound (5 weeks 6 days)

Pauline
I know that I am unable to get a clear, correct answer in regards to my situation, but it makes me feel better when I discuss it, because it's the only thing I can do while impatiently waiting until next Friday to arrive. Here's my story:
Based on the starting date of my LMP, I should be 5 weeks and 6 days today. I was brought in for a transvaginal viability ultrasound today, due to being labeled high risk (suffered 3 losses in the past, uncontrolled diabetes, age). The ultrasound tech could not find anything on the ultrasound...not even a gestational sac. She said my "uterus is empty", but it looks like its "preparing for pregnancy". The doctor said my lining is thick. I wasn't trying to hear any of that, because after seeing nothing there, I immediately went into panic mode. Two days ago, my HCG levels were in the 700s.  I was told that this was normal based on how far along I am. The doctor said it didn't make any sense to retest at this time, because it wouldn't tell them anything differently.  So, they scheduled me for another ultrasound 1 week from now. They further stated that I'm either too early or will miscarry, but again, they could not tell.
Now...I'm trying to figure out if any of the following data points make any sense OR is relevant in anyway to my situation's possible outcome. (I guess I'm trying to make myself feel better.) 😊
1. With my prior pregnancies, I have always been able to find out if I'm pregnant 6 days prior to my missed period using a First Response.
2. I tested early this time around and got negatives...almost wrote this off as just an abnormal period.
3. My period was supposed to start February 15th, based on Glow's predictions. I wasn't able to get a positive test until February 17th.
4. Based on Glow's predicted fertile window, my husband and I had sex days 1, 2, 3, 5 and 7. (We were on a cruise, so spending time together was easy...lol.) 🤪 My fertile window was January 27th - February 2nd.
Can any of this mean that my dates are off OR is this not enough data to tell?
Also, anyone else out there experienced this before with a successful outcome? I'm so ready for next Friday to get here so I can move past this.  Any feedback or thoughts is appreciated.