I was diagnosed as an adult and had to insist on having the tests. So should you you will feel so much better. I didn't really know how rubbish I was feeling until I started to take control and feel better.
There will almost definitely be some diabetes education near you and that's the game changer.
Your eating **** could possibly be explained by the fact that depending on your brand and portion your chocolate ice cream (say three small balls) could be around 30g of carbs whereas a large jacket potato baked could be around 90g of carbs. That is of course unless your having both.
Just a possibility. If you have a smart phone there is an app called 'Carbs & Cals' which i find really useful. If not there is a book version.
Good luck