Has your pediatrician screened out any possible medical issue? There are organic conditions that can cause behavioral problems in kids, and my perception is that the psych professionals tend to "stay in their own lane" and not investigate whether the behavior/mood issue could have an underlying medical cause.
Our story is VERY similar to yours (sweet kid with crazy-disrupted behavior). Turns out that DD12 had severe celiac disease, probably since toddlerhood. Getting that diagnosis and addressing related nutritional deficiencies has been a game-changer. She still has issues but it's a LOT better. Happy to share details / answer questions by PM if that would be helpful.
FWIW, we consulted about a dozen counselors, therapists, psychiatrists, developmental pediatricians, OTs, etc. about complaints of anxiety, irritability, sleep issues, stomach aches, head aches, mood swings, increasingly disregulated behavior, aggression, epic meltdowns, depression, suicidal ideation ....; pretty uniformly, they diagnosed an anxiety disorder/depression and recommended medication, therapy, etc.
Finally, a CBT therapist we brought her to for her anxiety said she'd seen her kind of sky-high anxiety only a few times before, and in a couple of cases the kid had been celiac so maybe we should screen for it. We did and were shocked by the result (off the charts positive) as DD isn't the picture of a "classic" celiac kid - she's always been tall, ahead on milestones, not skinny, etc.
To be clear, this is not to say that your son's behavior is attributable to celiac - but please make sure that you push your pediatrician to screen for that, thyroid, etc. (anything that can affect behavior in kids), and even if celiac is ruled out, consider doing an elimination diet to see if there's an underlying food intolerance.
Good luck - it's really hard. Your son is lucky to have you as a parent.
