Hello and welcome to the forum
I have been diagnosed 5 years and on a pump too, I don't have the pressure of GCSE's though, but if I did I would try and find a way to release some of the stress associated, so take a long walk or do some exercise, if your not doing this already, try and talk to someone around you about what each day is like and how you are coping. I know exams are stressful so managing both is a lot to handle, talking about how you are coping will help but try and set aside some time to manage your pump and insulin, keeping a good range will help you cope better mentally for your exams, try a mindfulness breathing exercise from YouTube too , good luck