Hi Dot, sounds like the joys of teenage hormones!
Perhaps he could check his sugars a few times between dinner and bed for a couple of nights, to see if he's climbing towards bedtime, or if it peaks a couple of hours after dinner then drops. if thats the case, he could be going low through the night and self-correcting? (can result in being more groggy / thirsty / headachy than usual in morning) Perhaps check his sugars through the night yourself a couple of times to prove/rule it out?
May just be the insulin needing tweaked as you say - when does he take his lantus? If its during the day it might be running out? (I used to take mine at night but would be high late afternoon, I increased dose and split it - 2/3 before bed and the other 1/3 in the morning and its helped readings a lot.)
NB speak to his diabetes team / dsn etc before you make any major changes. Also, I dont know your son so am not accusing him of doing anything wrong, but I remember going off the rails myself at 13 or so - rule out any changes in his diet on his part first (snacking before bed without telling you / eating too much / wrong foods?) Again your dsn will be able to guide you on how to adjust for this, could just be a boost of short acting insulin he needs to cover what he's eating (if applicable).