chest pain composes a wide spectrum of diseases depending upon side,duration,type etc.
common causes of chronic chest pain
,post herpetic nuralgia(usualy in aged),stress
and some psychiatric causes.
pain for 13yrs begining in childhood is realy painful.
you need not worry.
you should undergo some investigatios like ecg,chest xray.
i think it will be a managable one.
please consult a doctor expert in medicine/doc dealing adolescent problems.
hope it will help you.