Hi
I don't think you will find out definitively what caused your diabetes. All that really matters, is how well you control it.
Most T2 diabetics are overweight.
Instead of seeing a link, it's become popular to see cause and effect and hence BLAME.thus it's your own fault.
I am T2 also and overweight.
I think that the link is more subtle, that both conditions are caused by a genetic metabolic error, which begins before either condition appears. How else do you account for the 75% of overweight and obese people who are NOT diabetic and the ,admittedly fewer, Skinny T2s
Now how to g4et your numbers down
I prefer to let my diet do most of the work.
that is, cut out sugar, cut right back on, grains,(in whatever form) pasta, bread, potaotes, parsnips. In other words, STARCH.
That eill show an effect quite fast, Keep monitoring BGS and find out which foods push yours up. Your numbers are quite high, so you may well need to have VERY few Carbs. You'll be able to investigate this once your numbers come down into the "safe zone".
Get back to that GP and ask why you haven't been called in. they shouldn't let a diabetic slip through the cracks.