Hello i read your symptoms
Short answer: vitamin b12
Detail answer: Since you are a diabetic , and on metformin
Anti diabetics cause B12 deficency, so i suggest you to take b12 in the form of methycobol preferably injections as VIT B12 is not absorbed by the stomach and intestines.
Also if you were a vegetarian , i would definately presume you to have vitamin b12 deficency.