Diets are bad, figure out what foods you like, work around your life and that you enjoy.
Find some form of exercise that fits into your life, when starting an exercise regime go very slowly, remeber, slow and steady wins the race.
Finally no matter what, DONT GIVE UP. If you have a bad day, think about WHY it was a bad day, what you can learn not to do next time and move on.
I wish you the best of luck kid, you can do it