Hi Shaun and welcome to the club you never wanted to join!
I was also diagnosed with type 1 aged 18, so I've got a rough idea how you must be feeling.
That was a few years ago now and things are so much more sophisticated now. There's now no reason you can't become fitter, stronger and healthier than you ever were before.
For a start, this place will teach you all you ever need to know about how it all works. These people have seen and done it all, and are happy for you to learn from their mistakes.
Take a look around the forum and post or PM anything you'd like to talk about.
Al the best,
fergus