Hi Helen and welcome from me too. We all know what a shock it is to get this diagnosis and it will take several months to get your head around it. This forum is a wonderful resource to help you with that and many of us have found the support and information and advice we needed here where it was lacking from the health care professionals.... That is not necessarily a criticism of them as they have limited resources and this is such a complex condition that it takes time and trial and error for us to get our heads around what works for us and they can really only give general advice, some of which will not work for you and some is outdated.
Sorry to hear you are having a rough time with the Metformin.
I agree with
@SueEK that taking the Metformin with a substantial amount of food and I found swallowing it mid meal so that it is sandwiched by food in your digestive tract is important to prevent irritation. The symptoms do sometimes settle down after a while but if they don't, as
@KARNAK says, a slow release version is available which helps prevent these effects. The reason it is not prescribed from the start is that it is more expensive, so they try people on the "bog standard" stuff first. Discuss it with your DN if the symptoms don't settle down.
Something else to ask your DN is for your HbA1c reading. This is the reading which designates you as diabetic and gives you (and us) an idea of where on the diabetic scale you are. This is important because it indicates how radical you need to be with your treatment and dietary changes in order to reduce it to normal levels. Below 42 is normal. 42-47 is prediabtetic and 48+ is fully diabetic but that can go up as high as 150 or perhaps even higher although you would likely be extremely unwell and probably hospitalised at those levels. My guess is that your HbA1c may be quite high because your nurse is taking you up to the maximum dose of Metformin quite quickly, and it is even possible that you are Type 1 and not Type 2 but that will only be determined if you do not respond to oral meds and dietary changes, and needs specific testing for Type 1 which is not routine.
In the meantime it is important to significantly reduce your carbohydrate intake... that doesn't just mean sugar and sweet stuff but also starchy carbs like bread, pasta, potatoes, rice, breakfast cereals and even porridge, as well as fruit. That may appear like there is nothing you can eat but actually a very low carb diet can be enjoyable once you get your head around it. Shout up if you want and meal suggestions.
Anyway, good luck with the Metformin and I hope your upset stomach settles down soon. We are here for you whenever you need advice or support.