Hi Danny,
When going over your diet, a couple of things stand out. The breakfast is extremely carby. In the morning, our insulin resistance is usually at its peak, and then there's something called Dawn Phenomenon to contend with. Our liver dumps glucose when we wake, to give us energy to start the day. So you're likely already high, and then you throw a lot of carbs on top of that... You could skip breakfast entirely, as some here choose to do, (myself included, I don't have breakfast until lunchtime, really), or go for a low carb breakfast like bacon, eggs, high meat content sausages, maybe some tomatoes or cheese tossed in for variation. Let go of the calories: It's the carbs we can't handle, so that's one worry less.
As for dinner, ham, tuna and cheese are low carb, but the bread isn't... Maybe make it a salad, or a ham/cheese roll-up with butter? Low sugar, high protein for your main meal sounds good, but practically all carbs turn to glucose once ingested, so it's not just sugar, it's starches too that will spike us. Peas too, for instance...
If you want to try a stevia/erythritol mix, they are okay in warm drinks. (One or the other is absolutely vile, the combination tends to work though). But you'll have to test to see how your blood sugars respond to artificial sugars. Some can tolerate them, some can't.
I don't know what the cancer means for your diabetes... Where it's located (pancreas would mean you're developing T3c, not T2, so would require different treatment than solely dietary), whether you need to up protein as it is, or whether there's medication in the mix that raises blood sugars too, but it's something to take into consideration. Co-morbidities can impact one another, after all.
All in all there's a lot to win here, changes that can bring your blood sugars down further. Because going up and down all day can indeed make you feel miserable. Getting on a bit more of an even keel, preferably with non-diabetic numbers, should make you feel less wrecked. Should feeling like that continue after you get a grip on the blood sugars though, look further, as it may not be a diabetes-related issue. Maybe it's side effects from medication you're on etc, and it would merit further investigation.
Good luck!
Jo
PS: Get a meter. You're flying blind now and you need to know what's going on. Test around meals, before, and 2 hours after the first bite. You're looking for a rise of no more than 2.0 mmol/l between the two. Also, if you're feeling decidedly off, check what your blood sugars are doing. If you feel wrecked when high, you know it's time to look into how to get those blood sugars down further.