Are you a new insulin user? As a T1 on insulin my (car) license was for 3 years from the beginning, but I'd already been on insulin for ten years when I got my first license (back in 1980).
I think the requirements depend on circumstances though eg HGV drivers have a very hard time...
Yes I’m new to insulin. When I spoke with DVLA they said car three years and lorry one year. Out my hands I use my licences to earn my living just feels like a bitter blow. Something I’ve had since sixteen and now forty nine. Joys of getting older.
It can be 1, 2 or 3 years. Have you had any hypo's where you've needed help, or any other medical conditions that you've had to declare to the DLA? Just reapply next year, and hopefully you'll get it for 3 years.