aww, girlie, exercise is always hard, no matter if you are in pain or whatever. Cheap food is bad for you, as you have stated. Have you tried those healthy choice things? Though honestly there is not enough food for me there in those things. Milk is supposed to help. Give you vitamin c and other stuff like that.
Yay for going to the gym; that's great!
As for the walking thing that's awesome too. I would walk for those causes too, though i know I would hurt way to much by the time that it was done.