When you are in a terrible state from bad breath psychologically, it's also comforting to know you're not the only one, thanks to posts like this.
I totally agree with you on the stress-induced immune-lowering. VERY important point! If you get a can nip what's driving anxiety/ stress, it would definitely be a great help.
Regarding geographic tongue, Traditional Chinese Medicine specializes in tongues and understanding what's going on in the body through looking at the tongue. I dont know if you've tried this option (and I know it's not that scientific - but I've spoken to a lot of people who say Chinese medicine is amazing and has really helped them). I just thought I'd mention it :)