Hi Brian!
Read very carefully everything that MGB said above ^^^^
She speaks the truth!
The good news is that you've decided to make a change in your life, your realize that the reason that you are heavy is because you don't exercise enough and you eat too much. Very simple notions, but ones that get lost in the nonsense of diet books and infomercials.
So take it slowly, particularly the exercise. I've worked up to 3-miles of walking a day over the course of a month, I won't start running until I've lost another 20 lbs, because I don't want to stress my feet and joints too much.
Do not starve yourself! I would take a guess that if you cut your intake to 3000 calories or more a day you would still lose weight at a reasonable pace without starving yourself, but spend some time researching this.
I say it a lot to people, but we all got this way because we have lost the balance between how much we eat and our activity level.
We need to learn to achieve this balance in order to avoid a lifetime of yo-yo dieting. It's like learning a language- you need to learn how to restore or achieve the balance gradually, in manageable bits for long term success, if you cram (try and do it too quickly or artificially) It might work, but you will forget what you learned and the weight will pile back on.
Make learning how to eat and exercise to maintain this balance your goal, and weight loss and health will be the lifelong result. If you make weight loss the goal, then when you do lose weight, you will have achieved the goal, but maybe not learned how to maintain the weight in the process.
I am an expert in losing weight. In my lifetime I would estimate I have lost over a thousand pounds by dieting, and I have gained every one back.
Now my goal is to learn to live my life in a way that ensures a healthy weight.
You are young enough to get this behind you once and for all and enjoy a long healthy and active life. We're all here to lend support!
You Can do this!
David C