Little girl measuring small

Had our 22 week scan on Friday and little girl is measuring about a week behind, landing her in the 6-7% percentile. Waiting on referral to specialist. Trying not to worry but it’s hard. Our last son was born with severe brain damage that happened somewhere in the 2nd or 3rd trimester but we still never knew exactly why. Period dates me due 12/28, but 10 week scan showed 12/31 estimate - so technically this scan is only putting her 4 days behind that. I had an awful first 19 weeks with sickness and never gained weight but have started to this last two weeks and appetite is back in full force (thank goodness). I’m 33. Still terrified- any suggestions or relief stories from anyone would be great. Also, I’m fairly “petite” 5’3” and build sits around 135-145lbs. My husband is tall and thin. I was a small baby too, about 6.8lbs and 19”. That was also a lifetime ago and my mom smoked and was 18 lol, anyways just trying to find some reassurance. Also noting, she is super active! I love feeling her kick around 🩷