Hello and thanks for the query
In my personal opinion I don't think it is due the the metformin or related to diet unless the blood sugar level has being raised. The chest pain
on left side with a person having diabetes, hypertension
and obese, must be ruled out that it is not cardiac. Consult your doctor and get your EKG and stress test
done. If that came normal need not to worry and pain can be managed by analgesic
drugs or hot fermentation.
You have many risk factor for Coronary artery disease so change your life style according to the need and try to loose weight. Hope you will consult your cardiologist and get your EKG and stress test done.
Best Wishes and have a good time