Dude, you're looking at a MAJOR lifestyle change. Have your doctor refer you to a dietary specialist. Your life probably depends on it.
Quik and Matt/PA are not trying to scare you.....but you need to listen to them. This is bigger than you (no offense). You are looking at a MAJOR lifestyle change. We can give you all of the "6 meals a day"...."exercise often" lectures we want (and some have the right idea), but no one here's life is on the line. Yours IS. These guys aren't trying to scare you.....but if you are....good. Being overweight is in some ways like being an alcoholic. My dad stopped drinking in his latter years......but the damage was done. He'd drank himself to death as a young man. He lost several years to alcohol.
Your body is having to work SO HARD to carry that weight. You're doing damage, every day. Being young.....you can still turn this around.....but you need some professional help to do so.
I wish you luck, but this is bigger than watching what you eat (on your own) and walking the block a time or two a week.
Go see your doctor. Tell him you want to be healthy. If your current doctor has never said to you....."You need to change....or you WILL (youARE)cut years off your life".....then I'd find another doctor.
Again.....good luck.