Baby measuring 2 weeks behind

Lisa • Little Boy 7/7/10👦🏼 Angel Baby 7/9/17👼🏻 Baby Girl 8/22/19👶🏼 Angel Baby 6/2/2021👼🏻Married 10/20/18💑

I’ve been having some spotting on and off for a few days. Doctor brought me in yesterday because I’m O- and require the Rhogam shot for bleeding. They did an ultrasound and there was a sac and a baby but baby was only measuring 5 weeks and 6 days and I should be 7 weeks and 6 days. They said it was too soon to see a heartbeat so I got no real answers yesterday. I go back in 2 weeks to see if baby has grown or if we lost this baby too. Trying to stay positive but it’s super hard!