Hi Nic - it's easy to say "don't panic", but really don't - please.
Get your formal diagnosis, then read up on here, there is so much wonderful advice.
Personally I would recommend Low Carb, a Full Fat, I've tried every diet out and believe me I was getting fatter by the day.
I was diagnosed in March this year, and the very unhelpful locum doctor said I'd need a miracle to reduce my diabetes without meds, he reluctantly gave me 3 months to try and deal with it myself - and I am, my progress is in my signature.
I still have lots of weight to lose, probably another 3 stone at least, but I can't tell you the difference I feel in dropping that first 2 stone.
Get a BG meter, I had to buy mine, and learn what you can and can't tolerate, you'll surprise yourself and those "medical professionals"