Dear friend, what you have its call pectus excavatum or sunken chest.
is a congenital abnormality, occurs in 1 on 300-400 births with male predominance, I surprice you did not know your condition since this cases are diagnose within the first year or age becoming more pronounced at puberty.
Some patients with pectus excavatum experience chest and pack pain, scoliosis is quite common with pectus.
Some people experience shortness of breath.
My son 13 yrs old have pectus excavatum and we know since he was on my stomach, he is very very skynnie (thats normal with this condition) even though he eat a lot, once in a while he complain about chest and stomach pain.
here in the usa the only cure is surgery but we found a orthoclinic in Brazil that do not do surgery instead they use a brace (like on the teeth) to make presure and fix the problem.
I do not know how you feel about this but sometimes my son in on depretion.
You are not alone.