any advice?

FTM so i’m not sure if there is even anything to worry about this is just what happened.. Is anybody else’s belly measuring weeks behind what they are? I’m 26 weeks tomorrow and my belly is only measuring 22 weeks.. at my last appointment 3 weeks ago (23 weeks) my belly was only measuring at 21 weeks.. so that means my stomach has only grown about a week in 3 weeks time... i’m almost a month behind and a little worried but won’t be getting an ultrasound for the rest of this pregnancy unless I️ schedule a private one.. does anybody have any experience with this and it ended up being fine?