I don't know. I haven't heard of muscular pains being associated with metformin. As far as the kidneys, the doctor needs to monitor you with lab tests that include kidney function. You should tell your doctor that you have now and explain what's going on. Ask him directly if he thinks it could be the result of metformin.
I hope you're doing better!
diabetes type 2 controlled by diet and exercise and
very low carb way of eating