toiletting, lactose, glucose, celiac please help!

My son is 6 and still in nappies showing no signs of toileting after numerous tecniques tried. (Sorry if too much info) he is still very loose 99% of the time, we have reduced his lactose which helps a little, was wondering if any other diet change may help? Has anyone exoerienced this? His diet is balanced as possible as he doesn't eat much meat but plenty of everything else and is always on the go!