I am so sorry you have been through so much mcsfriend. I think all of us here and those who just pass through my site have been through the mill - I certainly have, ME/CFS from age 11, a battle with MCS over a perod of 5+ years (which I won and gained hope from!), a failed marriage etc.
I wish I had spoken to you before you had immunotherapy as I had a similar reaction with EPD, which is a form of immunotherapy. It made everything ten times worse and this was being recommended by seemingly enlightened doctors in private practice.
You're correct that MCS is neurological in nature, as is ME/CFS and other invisible illnesses. Research is showing without a doubt that we have neural hypersensitivity to stimuli and show signs of limbic kindling - the extreme end of which results in seizures and epilepsy. This is why I have no problem recommending brain retraining programs as they are certainly on the right track with utilising neural plasticity to reduce the hypersensitivity.
MCS is not a psychological disorder but as your story shows, certain events that affect us strongly emotionally, can have an effect on symptoms and severity of the condition. I have no qualms about admitting when I've felt happiest in my life, it has become much easier to deal with ME/CFS and symptoms seem to reduce. This is no coincidence, it's biochemistry. Happiness (prolonged especially) releases hormones, neurotransmitters, immune chemicals (and more) that reduce the limbic kindling and hypersensitivity in the brains of those of us with these conditions. This is why in my reply to your other post I mentioned meditation as being the key to my MCS recovery... I truly believe it was and that neural plasticity and "molecules of emotion" (see Candace Pert, PhD's book of the same name) were the key.
I will reply again to this message ASAP and try to answer your specific questions when I have the time to do them justice and really help you. For now, please don't give up, look for the light, and have hope. MCS and your other sensitivities can be beaten!