I think the sugar is stimulating an overagressive insulin response, which in turn drives your
blood sugar low.
Metformin doesn't work directly on insulin levels, instead it makes your blood cells more senstive to the insulin that is circulating.
I think best approach is reguar healthy (fat, protein, and small amoutn of carbs) meals and snacks and continuing to avoid sugar.
What are your 2 hours post eating levels?