I wonder if it is the fillers used that is causing the problem?
I understand that generics carry the same active drug, but use different (cheaper?) fillers.
My daughter insists on the originals only, as she says that these are the ones that have been tested.
I asked my chemist if that was true, and he said that they have all been tested, but I have my doubts.
Get the original formulation if you can to avoid a reaction to different ingredients.
You may be one of the super-senstive ones, like my daughter.
She will start with a tiny dose of anything new, never the recommended dosage. She builds up gradually until she finds her limit.