Improving my diet

It's been advised by my doctor and my health team that I need to improve my diet for the sake of my health. My Coca Cola consumption landed me in hospital last year, I didn't realise at the time it was such a bad thing to be drinking but it turns out drinking multiple cans a day since my teens has now contribute to a fatty liver, which amazed me as I am actually a very thin man.

So with this and the way it's now affecting my body they have advised I eat and drink more healthy.

The trouble is I think it's an autistic thing because I've always ate and drank the same things for most of my life so far. My diet is mostly Coca Cola, jam sandwiches and chocolate. My girlfriend has been trying to help me improve my diet but so far not much luck in that department. It's been suggested I try and get a dietician but my GP said the wait list is long and I'm also anxious about seeing people as it's a stressful experience for me.

I would appreciate and be grateful for any help and advice you can give me on this matter.

Right now we're lost on how best to approach this.