I have been on IVIG due to both immunodeficiency and autoimmunity. I also did Rituximab for 9 months, but discontinued it due to the COVID pandemic.
My doctor is experienced with dysfunctional immune systems and has has success with carefully selected patients doing Rituximab. As far as I'm aware, he only prescribes Rituximab AFTER patients have been on IVIG for over 12 months AND treats and rules out any infections. If one removes B cells which can help fight infections, it could be dangerous as the body might not be able to fight. He was very concerned about the possibility of my catching COVID before my B cells grew back.
It sounds like your doctors may not be doing the best thing for you... It would be wise to question them very carefully before proceeding.
Hopefully, IVIG will be helpful for you this time. I hope your doctor is prescribing support meds with it, like diphenhydramine, ketorolac, SoluMedrol and maybe lorazepam (as a mast cell stabilizer? I also use boswellia and curcumin fir brain swelling.