Usually, individuals born with pectus carinatum
Treating his depression
and depression itself has caused him to be with no energy.
I understand that you are concerning as a mother; but you must be strong enough to face your destiny.
It is good that your son is being treated medically and psychologically. That will help overcome his depression problems.
Not being able to burp is not something to be worried about. If no bur, then, more farting is present.
Although being special, the anatomical constituents of your son can allow farting if no burping. Do not worry.
All the best to you and your son.