You stated your concerns very clearly.

Every single description of what you feel, have felt and all have been felt by everyone here. You described it very well.
Your IVIG nurses are right in that many have been told ‘It’s all in your head’. stuff by docs. How did you get so lucky as to get the right diagnosis? Am I right that you ARE still getting IVIG now? Wow, less than 6 months from that vague term ‘onset’ to getting IVIG is beyond super, really.
As for getting reactions, many folks do get them, and there are ways to avoid them [mainly pre-medication with Benedryl, some anti-nausea meds] and for that rash, most docs never heard of some steriod oitments.
Be sure to keep a note pad handy to record what brand & how much you are given…if it’s not on the BAG, there has to be a record somewhere [it’s a blood product and the pharmacy and infusion nurses have to know and keep records] IVIG products are kept track of, pedigreed and certified better than any other medication on earth! And you know how the military loves to keep pounds of records.
Ask, and be sure to see if you can find a way to look at and get copies of the records of your medical diagnosis and treatment for future use. I don’t know if the military ‘exempts’ itself from ‘privacy’ patient records access, but everything that’s brought the docs to the conclusion for your CIDP diagnosis can be extraordinarily useful to any future doctors you see regarding your history and then future treatment. What one remembers six months later in detail gets harder the more months that go by.
As you have read, other folks have had issues that may or may not be ‘work related’. For your inquiries, be super careful in simply asking as if you ‘just want to know!’ If you find yourself wheeled or dragged around and ‘your folder’ happens to be toted along with you…well disapper and find a copy machine! Just be sure to have a personal ‘tote bag’ to stuff your copies into!
It’s for now far more important to get all the records, even on how often your poop, to get the long term poop on your miserable, and soon-hopefully not so miserable state of pain.
I hope you get better. And SOON!