Driving License

No need to resit your test; it's just a medical check; if you can give contact details of a diabetes specialist who you see regularly (once a year counts as regularly in my experience) and don't report any problems with sight, hypo awareness etc, then you'll be reissued before the previous one runs out. Worth mentioning to your diabetes team when your license is due for renewal, I reckon - shows you're organised and aware of responsibilities, which can't do any harm to your cause, but not essential.

Good luck with your driving lessons and test when it comes.

No cost involved to you with renewal every 1, 2 or 3 years (3 years is most usual, unless you have complications or other medical problems); even if you need a medical, DVLA pays.
Happy driving