Well, I guess I'm completely out of the loop. I know you said Chewy was being aggressive, but I don't remember about the thryroid problem.
Angus has hypothyroidism and takes thyroid pills. Did your vet tell you what the name of his condition was? I'm with everyone else, I've never heard of a thyroid problem making them agressive either. Anyways, I just hope you can get all of this under control so you don't have to get rid of him or put him down.
Take Care
Anna