@Tombish89 First don't panic, but you have come to the right place, we have all been there and many of us, including myself with an HbA1c over 100 when we were diagnosed. Your HbA1c of 55 is not very much higher than the threshold of 48 for diabetes diagnosis, so need to change everything a once. Ask questions with the doctor, it is important to establish if you are T2 or T1. as these are very different.
Try to convince your GP to give you a blood sugar meter and test strips instead of medication assuming you are not taking them already.
You can say you want to improve you blood sugar levels with diet. Many here have achieved good results with lowering their carb intake.
Weight loss also helps and as you are big you could consider this. How did you lose 5 stones already? if it works, continue.
I've lost 10 kg by intermittent fasting, 2 days a week with only 600 calories, other by switching from less carbs to more fat and protein.
This can work as fat is more satiating and you don't feel hungry. If you restrict your calories only, your metabolic rate will slow down,
you will not lose more weight, possibly gain back and feel miserable. This is not sustainable and why most diets fail.
As an aside, such yo-yo dieting is a great business model, you can list all the diet companies yourself.
You haven't told us what you eat, so we can't tell you specifics, but at your HbA1c level, you might see changes for the better with smallish adjustments. As for what not to eat, I went cold turkey on fizzy drinks. These are mainly sugar. This includes orange juice, eat an apple or orange instead. I've banned all low-fat food from my kitchen, these are sugary, so not filling and make you hungry. I try to eat real and non-processed food, e.g. vegetables, cheese, eggs, fish and meat. I never liked triangular sandwiches anyway.
I hope this helps and let us know if you have questions and tell us how you get on.
Best wishes on your journey.