That is between you and your doctor. We can't advise one way or the other.
However, if you are expecting Metformin to reduce your BS levels by more than a very small amount you are wrong. It helps to a limited extent by helping to reduce the amount of glucose produced by the liver, and can help in reducing appetite and thereby weight loss. What it won't do is stop the post meal spikes. Only diet can do that. It is known as a safe drug and is supposed to have other benefits.
One thing you have learnt - your body can't cope with teacakes!