@Iona May Congratulations on bringing your HbA1C like that.
Do you have a Blood Glucose meter so that you can test the effect of your meals? If not test before a meal and then 2hrs after first bite. If your BG has risen by more than 2mmol from just before the meal then there were too many carbohydrates in that meal for you (or ones you can't cope with))
If you can reduce your HbA1Clike that with Low Carb, then you probably don't actually need the small extra help that Metformin provides. So since you are still finding Metformin tough to cope with, try cutting it back to 1 a day for a week to see if you can tell any difference.