Please believe in yourself! Do you have some people around you that can help support you? If not, there are people here that you can buddy with!
It's great to have you with us. This is a great community of people who are striving to lead a healthier lifestyle.
For me, it has really helped to consider this a lifestyle change. I've been on SparkPeople on and off since 2007 but every day is still a day when I have to choose whether to exercise or not, whether to eat healthy or not...
SparkPeople has a great page with hundreds of motivational quotes. Peruse them and maybe print some off (I have one stuck to my fridge right now!) Here's the link:
Many people here find it helpful to start slowly and make a couple things into good, solid habits (for example, tracking foods or exercise or drinking water). When those things are solid, then they add some more.
Explore the great tools here on SparkPeople and ask questions if you have any.
After you've gotten used to the tools, I would also encourage you to consider writing a couple of blogs. It can be a great way to share your success and your struggles, and get specific feedback and support from people who can relate.
Take care and enjoy your journey!