First of all, leave off the guilty feelings, such things are common with boys of your age. Next, if you feel that it affects your health, eat good food and do regular exercise. If you want to apply a break, do reduce the frequency as much as you can hold on. In case you break it once in a while, do not bother, that is how the teen life goes on, be happy and stop worrying.
Don't worry about it, it's normal, especially at your age. However if it's really bothering you, focus on a hobby or play video games.
Masturbating is usually only a problem when you get older, say in your twenties and are using it to avoid a relationship with another person. At your age, you shouldn't be engaging in sexual activity.