The first time I had IVIG I ended up with aseptic meningitis. It was diagnosed by symptoms - stiff neck, super painful throbbing headache, backache, fever all starting the evening of the second dose of ivig. I didn't have any testing and was prescribed a medrol dose pack which immediately relieved the symptoms. I've had ivig every month since and have had a headache almost every single time. Not as bad as the first but the neuro suspects it's a low level aseptic meningitis each time. Yuck. I'm sorry you've had this problem.