So I know it is just an ESTIMATE. but a week ago at my appt they said he weighed 5 lbs 11 oz and…

So I know it is just an ESTIMATE. but a week ago at my appt they said he weighed 5 lbs 11 oz and today the said he's only gained an oz and the doctor measured his belly twice for some reason but didn't say anything was wrong. Any ideas?? I just thought at this point they were supposed to gain like half an lb or some thing a week??