I feel like a complete failure.....

I don't  know what my problem is I can't seem to ever stick to a diet for more than a week even with the JM diet the food was amazing. We went out of town one weekend and thats when I failed when your driving 5 hours to a destination its so much easier to stop and grab a cheeseburger than it is to eat a salad in the car. I just don't know what to do we desperately are wanting another baby and have been trying since January and due to my weight it is impossible and I need to change I just don't know how anymore.