Hey, I am a 30 year old guy, I was big in HS too. Not a great experience for me either. Anyway, you are on the right track by talking to people about it. Try starting a diet diary here in the forum. Be honest on it. If you have a real Sh##y day, write it down. Get back on the horse and keep going. We all have bad days, you will too. Just don’t give up. You have not wasted your life by getting big, you still have a lot of life left, and even more if you take control now.
I think what would help you out the most would be a low carb diet with relatively low calories, most coming from proteins. Stay away from all breads, potatoes, and rice products. You need to keep your insulin levels low because you are probably insulin resistant. Insulin mostly responds to grain products. Fat cells need insulin to take in food. You don’t want that. If you look at how bariatric surgery patients eat, that is how you should model your diet (but not as extreme) eat frequently, but less food, and mostly protein foods.
Don’t forget exercise. You don’t have to go nuts, just change some things around in your lifestyle. Walk to school, or to the store. Just get out more! I think that is one of the most important things you could do. Joining a gym helps if you are motivated, but joining alone will just thin out your wallet if you don’t use what you paid for.
I have a medical background, though you should follow your physicians advice, I can push you in the right direction. Ask your doctor to check your thyroid hormones to see if that is causing your weight problem. Feel free to ask me anything, Im here for you man. Congrats on taking control, don’t give up.