According to NHS guidelines they should be weighing no sooner than day 5 as this gives a better indication. A 'short' tongue could be a posterior or sub mucosal tongue tie, very few are trained in looking for these even many lactation consultants. The HVs and BF support workers in this area have been trained to look for them but this is very recent and in most areas this is not the case. My sister in law's baby he just looked like he had a short tongue but he has a tongue tie it's just under the floor of his mouth. I would ask for baby to be reweighed tomorrow if possible though it may be the case weight has dropped a bit further this is normal as long as it's still within the 10%, and if it's still within the 10% it's unlikely baby isn't getting enough xx