and pain are common sides effects of metformin. But you didn't experience it with metformin before.
So i my opinion it may be due to diabetic neuropathy
which is a complication of persistent hyperglycemia
where the outer covering of the nerves are damaged. This causes burning pain, tingling & numbness.
So i would advice my patient to keep the blood sugar levels under control. This will help to reduce the progression of the condition. Nerve conduction study
to be done to diagnose and assess the damage. Drug like Gabapentin is prescribed by the doctor for symptom relief.