Hang in there. Life does get better.
Exercise does help - even if it did not help in the past. It is a slow process (unfortunately) but even just walking will help a lot more than it will harm. The same is true of watching calories. The specific programs you have been on may not have worked, but that does not mean that eating an entire pizza in one sitting (I am not saying that you are doing that; this is just a for-instance) doesn't help, either.
One thing you should look into is your beverages. Stop drinking soda and drink water instead. Even diet soda can be problematic. Water is considerably better for you. If you don't like the taste of plain water, something like Crystal Light is fine.
Replace whatever snacks you are currently eating with fruit or cut up vegetables. Most people do not get enough fruits and vegetables and this will be a way for you to get ahead of everyone.
And, talk to your pediatrician. Ask if she or he knows of programs you could join. Explain that what you have tried did not seem to work. Your doctor wants you to succeed and should have contacts in the area.
Best of luck to you. I was heavy for years and I know a lot of how you feel.