All I can say about motivation is that it comes from a mindset. You have to make an unrepeatable, final promise to yourself, recognising the responsibility of your commitment and the seriousness of it. Then, with gravity of your determination to make a lifestyle change, carve yourself the resolution to follow through and never give in.
Think of the future. Do you want to stay as you are, and in all likelihood get worse - more unwanted weight, decreased fitness level, poor health - or do you want a ride to fame and fortune with happiness and health following you on your travels throughout this adventure called life?
As with most things, dear Shelley, it's up to you.