The Metformin doesn't really have a direct impact on your readings like that. It takes time to build up in your system and has a slow long term effect over days and weeks rather than an hour or two after taking a tablet.
except I was busy the other day so I didn’t eat much at all except for 2slices of toast with butter, brown bread before my dinner
Are you saying you had 2 slices of brown bread toast before your dinner yesterday? If so, how long before. If it was within 2-4 hours, then your pre and post meal readings were a waste of time because the carbs from the toast will totally compromise the test... which is why your pre meal reading was so high at 11.4.
If you are hungry whilst you are waiting for a meal to be ready, try a boiled egg (always worth keeping a few boiled eggs in the fridge as snacks to fill you up when you get the munchies with a spoon of mayonnaise or have a chunk of cheese which are pretty much carb free rather than a carb rich food like bread.
Apologies if I have misunderstood and the 2 slices of toast were at lunchtime and there was no bread or toast eaten before dinner.
It does look like you are eating rather a lot of bread still. It really doesn't make that much difference to your diabetes whether it is brown, white or skyblue pink, the carbs in it turn to glucose in your digestive system. Wholemeal is healthier for your digestive tract because it contains more fibre, but bread is a high carb food which will raise your BG levels and therefore adversely affect your diabetes.
Not saying not to eat bread at all, but limiting your intake is important.... Maybe just one or two pieces of bread per day and look out for lower carb options like Livlife. Maybe ration yourself to just 2 pieces of bread a day like one slice of wholemeal and a pitta or naan, or two slices of wholemeal and no pitta or naan, but not at the same meal and see how your body copes with that.
You mention two poached eggs at breakfast. Did you have toast or bread with those too... or just the eggs? Maybe have on a bed of spinach instead of toast or have an omelette with a salad with coleslaw... I find I miss bread less if I don't have a runny yolk that needs soaking up, so an omelette works well.
Are you testing pre and post meal for your breakfast and lunch to see the effects of the bread in your sandwich?
As regards your BG levels varying. Non-diabetic people also have a constantly changing Blood Glucose profile and someone recently posted the graph of a non-diabetic fit active marathon runner which was plotted using data from a sensor which measures glucose levels every few minutes over the full 24 hour period and the results show how much of a constant battle is going on in the body to keep levels within quite a broad range.
I will see if I can find it and post it....