Hello Helen and welcome to the club.
Please don't expect miracles from Metformin. It is a good safe drug that most type 2's have, but it isn't a cure by any means and has limited effect on your blood sugars. It just helps your liver a bit and is supposed to suppress appetite. Worry not about the initial side effects as this is normal, but if you are still suffering after a couple of weeks or if it gets a lot worse ask your doctor for the slow release version as this is more gentle. I'm not an expert on Metformin as I don't take it, but have picked up from what many others on the forum have said.
The only way to reduce your blood sugars is by changing your diet, adding some exercise and losing weight (if you need to). Metformin won't do this for you, it is all down to you and a life-style change. There is a lot of help and advice on this forum, written by people with diabetes. Have a good browse round, look at the low carb threads and make a plan of action.
The NHS advice is very poor, and mostly wrong. All carbohydrates turn to sugar once in your system, not just sugary foods. Carbs = Sugar. The less you eat, the better your blood will be. You need to be aware that starchy carbs are the very worst - bread, potatoes, rice and pasta, pastry and batter. No-one is saying cut these out altogether, but reduce your portions drastically. You can eat fruit but need to be very careful which fruits you eat. Berries are the best - raspberries, blueberries, strawberries etc. Avoid tropical fruits such as bananas and oranges, and avoid all fruit juices.
Please ask any questions you like, and don't panic. Baby steps to begin with.