My A1c was 5.3 last year, (I am due another), and in consultation with my DSN I started on Metformin! OK, only 500 mg a day, but nonetheless it is in direct contrast with your treatment.
Whilst agreeing that the doc/DSN is always right, I also believe that some are more right than others.
In my opinion, to stop your Metformin completely does not add up, it is a very safe drug and has known protective effects apart from increasing sensitivity to insulin.
I would make a docs appointment and get a second opinion, I would also argue the case for continuing Metformin maybe with a reduced dose.
Putting my crystal ball gazers hat on, I would foresee rising A1c s in the future, probably needing medication, and it is a fact that Metformin is a lot more effective when started early rather than late. That is the main reason I was started on it.
H