I would join "Tongue Tie Babies Support Group" on Facebook...4 months is not too old at all. The group has a list of reccomended providers, because not all ENTs/dentists etc are skilled at diagnosing and treating posterior tongue ties even when they think they are. It's not always an immediate improvement, but, you will probably notice some soon after and then continued improvement over time. The procedure itself is just minutes, and if done by a skilled provider will not be done with any type of sedation or anything.
ceceb, Did you join the facebook group? They have a recommended provider's list of professionals who have a good reputation for treatment outcomes (the 12 month old had no anaesthesia snd the 5 yr old had local only). A posterior tie should be treated by laser with NO anaesthesia, so the latch and nursing can be assessed right away.
Just had both my kids lasered (lip and tongue) by a dentist with good results.
check out this resource: www.kiddsteeth.com
And don't ignore the lip tie!!!