I'm sorry to hear that you're worried about your weight, but first of all, it might be an idea to get checked to see if you are overweight (for someone of your age/height/gender) or not - you could ask at your diabetes clinic, but you could also ask your GP or school nurse if you have one.
People have very different perceptions of what is the right weight to be and though you think you are putting on a lot of weight, you may in fact be of an acceptable weight, which is why it is best to get clarity on this from a healthcare professional.
If you do find you need to lose weight then your doctor/nurse should be able to help you do this and advise you of how much it is necessary for you to lose - they can also arrange for you to see a dietitian who will give you specific advice on how you can adapt your eating habits.
Although it’s important that you think about what you eat to manage your diabetes, you should still be able to continue enjoying a wide variety of everyday foods as part of a healthy diet. In the meantime, if you are having problems knowing what is going to be a healthy snack, you can have a look at some snack ideas on our website here:
You can also have a look at the following link to the Change4Life website from the department of health; which has details of how to eat healthily and suggestions to help you get active, with specific advice about what is going on in your area.