One thing which I always try to keep in mind is that insulin operates over time. That shot you have for lunch will be working at various rates for about the next 4 or 5 hours, peaking after about 1.5 to 2 hours and then gradually tailing off. So when deciding how much insulin to take for a meal, you need to not only figure out how many carbs are in it but also how active you're likely to be for the next 5 or so hours as that too will influence the amount of insulin.
Because you're basically trying to balance insulin, carbs and exercise, it means that if you're going to be sitting in front of the telly for the rest of the afternoon, you might take x units, but if you're planning on going for a run later, you'd likely want to take less insulin for the meal as your body has ways of using glucose without insulin when exercising, so the combination of exercise and insulin can be a double whammy.
If you've exercised before the meal, you can sometimes get a delayed "after drop" so you might need to take that into account tp and maybe tail back the insulin a bit.
And if you were planning on doing a run 2 hours after the meal, remember that that would coincide with peak insulin action, which would get messy.
Basically, anytime you're doing something active, have a think about how much active insulin you still have on board
Certainly doesn't mean you can't do them, just requires a bit more planning ahead, and accepting that there are some inherently unpredictable aspects - your liver's got a mind of it's own and will sometimes release or take back glucose without bothering to ask you.
Ask the hospital whether they'll give you a free trial of a Freestyle Libre. Some do, some don't - it's a bit of a postcode lottery. It's a small sensor worn on the arm which measures glucose levels continuously so you can see a continuous graph of where you've been for the last 8 hours and will say whether you're rising or falling rapidly, which is a huge help in anticipating hypos and then taking some carbs to stop it happening. Strips just give you a little snapshot of a point in time, which is not that much help when you're tracking a constantly moving target. Libte is like seeing the whole movie. It makes life a lot easier. Not on the NHS at the moment, so it's £50 for 2 weeks. There's also dexcom which gives alerts, not sure of the pricing for that.
Best of luck, I took things easy for a few months after dx, but then got back on my bike, skis and boat and had a pretty active life.
