No-one on here can say if you've got a good case for appeal as we a) haven't got sight of all the relevant information and b) won't go making suggestions on medical issues by doing some kind of online diagnosis. Neither can the staff in an AFCO help with specifics as they aren't medical specialists.
As an ex-RAF Recruitment Officer, what I can say is the evidence for an appeal has to address the reason for the rejection and provide information that is new or in addition to that in the medical records.
Medication or hospitalisation (or not) aren't always issues; it can be factors such as the stressor, the type of reaction to said stressor and how many times it occurred. The Armed Forces all work to the same fundamental medical standards, which are based on research and the likelihood of a reoccurrence, given the conditions of training and the job. Hence they are not going to take a risk on someone who may not cope with military life, no matter how well that person may be coping with life as a civilian, and there are always other candidates that do meet the entry standards and who can be selected for recruitment.
That's as much help as can be given and sorry, unfortunately it may not work out for your son. That's not to say you shouldn't try if you have acceptable evidence.