That problem with sweating does not happen to me. My body's reaction after IVIG is inconsistent and subtle. I could never state anything definite like you've done. I have a mild headache some of the time. I notice no improvement immediately, However I am improving in some aspects on a very slow and not steady trend line. Those things being strength, footdrop, balance, endurance, I have a ways to go in each of those for sure. I do rehab exercises religiously and push myself a little at least a couple times per week. There is a fine line on that of how much is too much.
Do you drink the large amount of water that is suggested the day before, the days of and the day after IVIG? That might help. When was the last time you had a Chemistry Panel? I would have one if you haven't had one since this started to happen.
Best regards.