Hi
@Lizzypier , welcome back.
We cannot advise on going against the advice you have from your GP on prescribed meds. However, nobody is forced to take prescribed meds if they choose not to.
In your situation, I would probably want to lower my BG as soon as possible to enable the surgery to go ahead. I am, in fact, due to have parathyroid surgery soon, so being very vigilant about my own BG levels.
Metformin will possibly help, but not as much as altering your diet. I still take it, along with low carbing, and maintain for several years HbA1c of between 41 and 46 apart from a high of 55 when I was very ill a few years ago.
It could help to get opinion from your surgical team. Such as info on the timescale for the expected surgery, and criteria for the BG HbA1c they require. That might help you decide on your method of lowering those levels.
Your GP could have been a bit more helpful. Some people do get abdominal issues with Metformin, so need a slow release type. I have been fortunate not to have those symtoms and get along just fine on the standard version.
Best of luck, whatever you decide, and please keepus informed of your choice, and your progress.