That depends on your T's training. Unless he is a clinical psychologist or a psychiatrist he won't have the expertise/training to diagnose.

Psychiatrists are typically the go-to person if someone wants a diagnosis (and meds).

*If* he is a psychiatrist and failed to diagnose you then it's a different matter. Things to bear in mind, diagnoses can be somewhat subjective (or at least not as objective as they claim to be) and/or he lacks the experience of your older psychiatrist.