Firstly, be careful when taking advice from a forum - We are not medical experts!
I'd sugest that you go and speak to your doctor, a nutritionist and a sports trainer. Possibly also worth speaking to a physio/massage therapist - no good doing massive exercise if you end up hurting yourself. If you can't afford to get appointments with people, ask your parents or hustle to get these people's attention. If you show you're comitted to losing weight, people may help you for free.
That said, I'd point out 3 things:
1) Food: you cannot outrun your fork. Experiment. Some people swear by the Paleo diet (not a diet - its a method of eating), some say carbs are best. Either way, eating smaller portions and eating it slower will make you feel full without overeating. [Blog suggestion: Nerd Fitness]
2) cardio is good for some, but I've personally found that weight training is better. Then again, I dont do any of this unsupervised becuase I don't know enough about fitness myself.
3) A lot of food is psychology - work out why you want to lose weight, why you (may) overeat, what personal things are going on in your life, if you smoke etc.... and this matters more if your problems are not medical i.e. there are some people who find it very hard to lose weight becuase of unknown medical issues.
In the end, what works for one won't work for everyone.
I'm making a curry tonight, which I've made thousands of times before, and I have worked out that in a relatively small portion (well, by my previous standards) there are almost 2,000 calories, which is more than enough for me for an entire day, let alone just one meal. So there are more calories in things than you think. Add everything up and you will probably be surprised.
I swear by the paleo/primal lifestyle. I've been living this way for several months now, so it's not a fad but a way of life. Check out mark's daily apple: http://www.marksdailyapple.com/#axzz1ynw9YYSn if you're interested. The worst foods to eat are refined sugar and grains, so cutting those out will make you drop weight instantly. They carry no nutritional benefits to us and cause problems like diabetes, heart disease, auto immune diseases, etc.