I was thinking about your son. I am wondering if his "Verbal vomiting" is a compulsion. Confessing is a compulsion, maybe this is a compulsion. My daughter used to "confess" all night long until we figured this out. We needed to help her stop. If it is, you need to use strategies. Maybe let him only express his worries for a certain amount of time or only express 5 worries at a time. Then go down to less time or 3 worries at a time. Then less, etc. My DD has had weird compulsions. She goes to Dr. Chansky, who literally wrote the book on childhood OCD. She also recommends talking back to OCD sarcastically, like - "Thank you so much OCD for making me worry about all of these things. You are sooo smart. I wanted to think about football, but this is so much more fun. What would I do without you?"
FYI - We saw her during a bad flare last allergy season. My daughter was using her strategies, but the OCD would not stop. She said when a PANS/PANDAS child's immune system is so taxed, CBT will not work.
In regard to my earlier post about Dr. Swedo and antihistimines, she did not expand upon that statement. All I know is that antihistimines block the H1 receptor, the receptor that causes inflammation.