I had a really bad diet when I was a kid... Parents didn't have much money, couldn't cook very well, and cheap fast food is horrible for you, etc... And by the time I was thirteen, it was highly recommended that I change my eating style because I was pre-diabetic and had high cholesterol and such. Since then, I've been avoiding white bread, sugar, etc., and I even write down everything I eat. I really wish the unhealthy stuff wasn't so prevalent in our society!
It gets better over time, especially if you try different sorts of vegetables. For example, I hate most raw vegetables, but take me to Ruby Tuesday and I'm super excited about their spaghetti squash and broccoli.
It's also a good opportunity to try some foreign cuisine... Maybe not something like Mexican with its heavy emphasis on carbs, but possibly Japanese restaurants (ask for stuff without white rice) Indian, or Thai ones.
It takes a while to stop craving sugary fast food stuff, but now I'm glad I don't like it! I used to mainly eat Burger King, McDonald's, KFC, and was too "afraid" to try a lot of other foods that I now enjoy. I'm by far not the fittest person around still... I'm not running a marathon any time soon, but a lot of my health problems are gone.
I didn't mean to give you my life story, but I just want you to know you can still be optimistic.