Normal for baby to measure smaller at early ultrasound ???

I went in for my 6 week ultrasound last Tuesday and I was told that baby was measuring at 4w 5d instead. The doctors aren’t concerned but I am due to knowing my cycle pretty well, regular periods and as far as I know I usually ovulate on CD13/14/15

If my dates are wrong then I would have ovulated on CD17 or so to put baby at the date they gave me at ultrasound. Maybe. I’m not even sure.

When I tested on day of expected period, my lines were super faint. And they have only gotten darker since. I’m now testing with dye stealers, so dark that the control lines are losing colour. Not by much but they’re cheap easy@home strips and I know they take forever to develop/progress etc etc.

Anyways.. my symptoms haven’t been super strong since I found out. I hardly feel nauseous, only here and there after a couple days in between, my breasts do feel heavier and feel a little sore here n there (or when I give them a lil squeeze), I am way more tired everyday, as if I smoked a bunch of weed (I’m not smoking weed at all obviously), dreams have been WILD and that’s putting it lightly lol... so I have symptoms but I’m just worried anyways. I have my second ultrasound tomorrow, which would put me at 6 weeks on their dates.

Is this normal? Should I be worried?

My last pregnancy went well up until I gave birth and my daughter ended up having turners syndrome and was stillborn. The diagnosis has nothing to do with our genes, we were both checked.

I’m scared that I’m going to miscarry. Or that because baby is measuring small that there won’t be growth or a heartbeat at this next ultrasound. I’m anxious beyond belief.

Please share stories of your experiences with baby measuring smaller.

As I said the doctors are not worried, there was a gestational sac with “a tiny structure inside” and the “yolk sac was not well seen at this time”.... they think I ovulated later in my cycle and that this is “very common”.