Hello Hiocherryo,
My first word of advice is - breathe. Absolutely low self-esteem will make achieving any goals more difficult. Depression tends to warp our perception, this I know from personal experience. I recommend that you talk to someone you trust regarding your feelings, your weight, overall health, and desire to make changes. Consider a parent, aunt, teacher, school counselor, your dietician, friend's mom even. Just some possibilities of people to talk to.
Since I don't know how tall you are or what your body percentage is, it is impossible to know what a good goal would be for you personally. To calculate some of these pertinent numbers, go to the Getting Started page. However, this information is geared for adult bodies. I honestly do not know if anything differs for younger teens.
As far as significant weightloss, I can tell you that even a loss of 5-10% will make a difference. Wanting to jump right to 130 lbs from 200 lbs is too difficult of an initial goal.
Try this: start journaling what you eat and what physical activities you engage in. Nothing fancy, just begin writing things down. Your dietician can help you with ideas here. Be sure to measure your body: height, weight, waist, hips, neck, upper arm, widest point on a thigh, widest point on a calf, etc.
When you have dropped 5% (or 10 lbs), give yourself a huge pat on the back. When you drop 10% (or 20 lbs), remeasure yourself and see how things may have changed. Be sure to eat ENOUGH food and drink plenty of water so that your body has enough energy to function.
This most you should probably think about losing is no more than 40 pounds. That would be a 20% weight loss from your starting point and this will make a HUGE difference in how you feel physically. But since you have other medical conditions which might complicate things for you, you MUST talk to your doctor about ALL of this.
I'll say that again. You must talk to your doctor and your dietician.
As far as foods or exercises which might be good for thighs or belly...if you like swimming, try that. It is the only thing which has ever toned up my thighs and abdomen while helping to make them feel slimmer. Again, talk to your doctor please.
If you have any other questions, please feel free to ask.