I do not recommend IVIG unless you have a neuromuscular disorder or have tested positive for neurological antibodies and even then i would be reluctant to advise doing it. There can be some real bad side effects inlcluding aseptic meningitis which i have had several times from IVIG. You don;t want this!
You also run the risk of picking up weird infections that may be very difficult to treat or more so very difficult to diagnose which would mean you are not gong to get help for it. Plasma protein is also capable of transmitting all sorts of diseases, infections, viruses, ect.
Docs will tell you the IVIG is filtered and donors are screened but that does not mean it is true. These are the same folks that hand Cipro or Effexor and tell you there are no side effects. It is not worth the risk.
Any benefit you get will likely be temporary and subside after the IVIG leaves your system. You will put yourself at such great risk all for something that is generally not lasting. Unless you have Myasthenia Gravis, LEMS, Guilain Barres and other serious autoimmune disorders i would not do it.
There is no proof it will help chronic fatigue type symptoms. You need to figure out where your chronic fatigue is coming from, not mask it with IVIG. IVIG can also re-moddulate your immune system to attack you, which would basically be giving you an autoimmune.
Could allow opportunistic infections or viruses in your body to reactivate. The list goes on and on. I usually don't post here, but when i saw you were considering this i felt inclined to give you some perspective.
This is just my opinion but i think you should now what you are getting into. Docs don't always disclose all the risks, and more so they don't understand the risks cause they have not done it.