To answer your question about staying motivated, here are the most important things I've seen:
1) Small steps to build momentum truly does work and can transform your life. Each small positive step you take can build momentum -- and then the more momentum you have the easier this gets. So even 10 minutes of exercise at a time -- walking to your mailbox and back, walk around the block, etc. can literally lead to changing your life. Eating one more serving of veggies, etc.
2) Think about your big picture goals and why you want to be healthy. Then, continue doing this with each step you take because as your momentum builds, your goals might build as well.
If you'd like more detailed thinking on this, my book The Spark is an incredible companion to the site and many members have said the book has changed their life.