It is hard. And then comes a moment where it all just clicks into place and things start to make sense, believe it or not. The main carb-heavy foods to avoid: Fruits, except for most berries, tomatoes, avocado and starfruit. You having berries with yoghurt was actually a step in the right direction! You want the yoghurt to be full fat greek yoghurt though. The fattier something is, the more it'll slow down the carbs you do eat, and it's just about the lowest carb yoghurt out there. No spike = no damage.

Anyway, stuff to stay away from: anything made with flour. So bread, wraps, buns, pasta, cake... All of it, not good. Same goes for corn, cereals (yes, even weetabix), rice and potatoes. Anything starchy is out, as starches are carbs. Sadly that also takes out a lot of the underground veggies and legumes. (Though some are okay with legumes... Your meter'll tell you!) That sounds like I just told you to bin all foods ever, probably. But eggs are fine, as is meat, poultry, and fish. Cheeses are excellent, as are above-ground vegetables. If you've read the Nutritional Thingy I shared earlier, maybe use it to sort out a new grocery list...? It helps if you do it at home, because you don't want to be stuck at the supermarket going over labels for 2 hours straight and coming home with half a bag worth of air. Find brands you can swap, things you can replace etc... Easier at your desk than it is in the shop.
Your three month test, as you put it, is your HbA1c. I have no idea what 11.8 would be, as I am usually dealing with a different measurement and I don't know what units or percentage were used. And usually when i try to convert something I mess it up, haha. But your fasting blood glucose I do recognize.... And 15, that's pretty bad. Good news being, that you can totally come back from that. I did. So did many others here with me. It'll take some work, and a steep learning curve, but you can get your numbers back into the normal range. Getting a meter of your own would help enormously with that, so I'm tagging
@Rachox in for some of her excellent info. Right now, getting your numbers down, if you're at 15 mmol/l when fasting, is going to take some time. Normal blood glucose readings would be between 4 and 7, and preferably never over 8,5, as that is when damage starts occuring. (
Don't panic, you'll be okay). It'll take a little while to get this under control because your liver thinks you should be higher, as that is what you're used to, so your fasting blood glucose will remain relatively high for a while because your liver tends to dump glucose into your bloodstream to get you back to where it thinks you should be. So what you should aim for is a rise of no more than 2.0 mmol/l between before a meal, and 2 hours after the first bite. If you keep that going, your fasting blood glucose'll come down too.
All in all, it's a lot to learn. I know when i was first diagnosed and completely overwhelmed, besides terrified, it helped to take notes and underline things, so i could keep going back to them until my brain finally let them stick. Diagnosis is traumatic, your memory can actually get a bit of a knock. So maybe put a list of okay foods and no-no's on the fridge for instance. Repetition helps things to stick.
Like I said, you'll be okay, even if you don't believe that right now. You don't have to get everything perfectly right overnight.
Hugs,
Jo