Strange...are you positive it's the whey powder? Could it be coincidental?
If you're sure it's the powder, it's possible that you're having a reaction to one of the ingredients (a preservative perhaps? it could be anything really). Not much you can do but discontinue use and try another brand....
If there is artificial sweeteners in a decent size dose that could be the cause. I know that sugar-free jello used to give me headaches all the time. Switch to an 'all-natural' source like the ON 100% natural whey and see if that helps.
Strange...are you positive it's the whey powder? Could it be coincidental?
If you're sure it's the powder, it's possible that you're having a reaction to one of the ingredients (a preservative perhaps? it could be anything really). Not much you can do but discontinue use and try another brand....