Hello, emptyshred

It very well could be about control. You said the psychologist was a bad fit....you may have to try several before you find one that you and your son can relate to.
There might be an area in his life he feels he has no control over. I would gently try to figure out what that might be. Did it start when the younger child was born or when he got a new teacher??
If it's any consultation....a few years back my grandson would not eat...even at fun places and restaurants we wanted to go to.(we would even let him choose) His blood sugar would get so low he would get headaches and instead of having a fun outing we would be in the ER. He was so skinny it was scary. I have a few theories "why" he went through this but the point is now, only a few years later, he's a fantastic eater...very athletic, and healthy.
Your concern is warranted...but you are taking steps to assist him. Enjoy the confort and support here on PC. I trust you will find some answers
Best wishes,