Fatty foods are not the only ones you need to eliminate from your diet. You should also not eat foods with white sugar or flour, such as candy, pastries, cakes, cookies, sodas , etc.
Are you getting plenty of exercise?
You may need to ask your parents to get you tested for hypothyroidism, if you do everything possible and still can't lose weight. Your thyroid controls metabolism, so if yours isn't producing enough hormones, your metabolism won't be right either. You would to be tested for Free T3, Free T4 and TSH.
Your carb intake can also be effective with your weight gain. if you eat a lot of fruits potatoes and starches can cause massive weight gain try a low carb diet and see if it works if you stick with it in that is your problem you will lose a 8 to 10 pounds within 2 weeks and if not then you might have a thyroid problem
Losing 8-10 pounds in 2 weeks is not safe. Safe weight loss is 1-2 pounds/week. You should be able to do this using a combination of healthy diet and exercise.