LilyAmaryllis what do you mean you've ruined it with a snack of cheese? Unless you know that dairy is an issue for you, cheese is a perfect low carb snack!
Molly welcome! Although you say you don't eat much it could be that your diet is simply too high in carbs for you to lose the weight. What is often seen as a 'healthy' diet is simply too carby for many of us. So the typical day:
Breakfast - bran cereal or muesli with skimmed milk, or wholemeal toast with low fat spread and honey, and a glass of fruit juice
Lunch - sandwich, made with low fat spread and wholemeal bread with a piece of fruit
Dinner - pasta or rice (possibly brown, because it's 'healthier') with some kind of low fat sauce, or a low fat protein-based dish with some plain veg
And no doubt a snack or too thrown in during the day - the odd biscuit perhaps, or an extra piece of fruit, because fruit is 'good for us'.
Does that sound about right?
I did a calculation once, when I was writing the low carb piece for the Diet and Fitness pages and worked out that this kind of 'typical' day would see you eating almost twice the amount that Dr Briffa would say we should be eating a day (100g) - and that's not including the carbs that you might have in any tea or coffee that you'd be drinking during the day.
On a low carb diet, or - more accurately, way of eating (WOE) - we are looking to reverse the proportions of our foods. So we change from carbohydrates:protein:fat to fat:protein:carbohydrates. It takes a conscious decision and effort to do this, because it runs counter to everything we have been told over the last 30 years or so. But it is a much better way to eat, IMVHO - and if there is an issue for you with insulin then this should help you.