Jenni,
I think it's quite common for kids to start having symptoms a day or two later. My daughter used to have IVIG weekly, and she would usually be nauseous and vomiting right afterwards, but the horrible headache and insane sleepiness would get worse gradually over the next 3-4 days. Because she had an anaphylactic shock reaction to her first infusion, they would always give extra Benadryl and Tylenol both orally and through the IV. They also slowed the infusion down to 14 hours. It kept her from anaphylaxis, but every time she would get deathly ill, usually for about five days. I would say she never really felt well at that time and she missed a ton of school. At the time, I thought it was part of ITP and didn't realize that most of her symptoms were as a result of her treatments and the medications. It's interesting to note that while Benadryl and Tylenol are the primary pre-meds given, if you look in the PDR you will find that they both have thrombocytopenia listed as a side effect. Hmm..maybe not the best choice for someone who already has ITP!
But, what to use instead? I have found homeopathic remedies to be a very effective substitute. Cancer patients going through chemo or radiation treatments have found good relief with homeopathic remedies to relieve the side effects of the very toxic drugs and radiation used. There are some good studies on this, and many of the top cancer hospitals are now encouraging their patients to use homeopathy, as they've seen that it can help. So, too, it can also help with side effects from IVIG.
You said your son's symptoms look almost like the flu.
That is how I would describe my daughter's symptoms
as well. Homeopathically, we should look at remedies that have a similar pattern of symptoms, and if you give it, it will quickly restore balance to the body. Here is a link to an article describing how powerful and effective homeopathy was in treating patients during the 1918 Spanish Flu pandemic:
nationalcenterforhomeopathy.org/files/neustadter_nov04.pdf
If you read further in the article, it describes the two remedies that were needed by the most patients during that time: Gelsemium and Bryonia. There are descriptions of other remedies as well. But, both of these two are known for a slow onset of symptoms, it comes on over a few days time (which is also the case for your son. )
The extreme sleepiness and weakness is a keynote of Gelsemium. They both have some of the worst headaches, too, but occur in different locations on the
head. The article differentiates them well from each other. Three others that are also worth considering would be Nux vomica, Arsenicum album and Hepar sulph. They each have certain indications. You can buy any of these OTC in a 30X or 30C potency and try a dose or two to see if it helps. Try to choose the one that seems most like his symptoms. Give a dose of 1-2
pills. If you see improvement, only repeat the dose upon a relapse of the symptoms. If there is no improvement after 3 doses, then try the next most-indicated remedy. If there's improvement but it doesn't last long, he likely needs a higher potency, like a 200C or a 1M, only available through a homeopathic pharmacy. Most of them require that you be working with a practioner for the higher doses.
Good luck!