Developing diabetes after having had gestational diabetes, usually means type 1 or one of the others that are usually diagnosed type 1 (MODY or LADA) If it presents as type 1 they won't bother to find out if it's one of the others. If you're insulin resistant at the same time, that's why they've put you on to Glucophage otherwise called Metformin. Metformin acts against insulin resistance. it does often cause "tummy grumbles" , but you adjust to it. you can help yourself with it by taking it half way through your meal. If that still doesn't help in a few weeks, you can ask your doctor for the slow release form, which is less "Grumbly", so I'm told. I've been using the ordinary one for 5 years trouble free. Your doctor is right, insulin is what puts weight on, but it does so by processing the carbohydrates you eat. So you can control your numbers better and your weight by dropping the intake of carbohydrates. If you're still eating sugary stuff. Get rid of it! also cut back on bread, potatoes, rice, pasta and cereals. We know that's what many dieticians recommend as the basis of your diet, but it doesn't work! Even our own Ally5555 admits to getting her patients to cut back. Lastly cut out junk foods and reduce portions. If you do it a bit at a time, you'll get used to it. As you cut back on food, you'll find you need to cut the insulin too. Keep testing and if your BGs keep going too low, you'll know to do that. While you're adapting, it might be a good idea to carry glucose tabs in case of a hypo.
Hope there's something there you can use