You are just a little too young to be on a proper muscle building program. That said, you need to eat quite a bit more, take a good protein powder and stick to incline benches which are better for building your upper chest than flat. Also incline flyes, done, as Arnold used to say, "like you are hugging a tree." Shoulder work is also key as you are basically trying to build up the upper area of your body. But at your weight, and if you were about 3 years older, you would easily have to put on 25 pounds to have some bulk to your muscles. Muscle building requires extra food and rest--both of which are often neglected, especially by the young and inexperienced.
