This is called Plagiocephaly. This problem is usually solved by itself in early infancy, as a part of normal growth along with assisted positioning of the baby during his or her sleep. If not resolved then some treatment like 'orthosis' can be done in tender ages.
I am very sorry to say but as you are 17 years old, it is almost impossible to get back that previous shape.
Anyway I will recommend you to visit a plastic & reconstructive surgery specialist for a further elaborated and detailed guideline.