I'm having the same issue... I have an rx prenatal that I'm still not sure about, but the pharmacist said he didn't see any of my 'bad' foods in the ingredient list. But after 2 months of an elimination diet and still some reactions in my BF dd, I narrowed it down to my calcium supplement!! Then while Googling the brand (Citracal), I ended up at the manufacturer's website where they say that vegetarians and people with food allergies should only take the Kosher version of their product (and especially not
the Citrical + Vit D) because there is no food product in it. So I am assuming that means there IS food product in the non-kosher version. Trust me, I looked at the labels closely before I bought these, and it says nothing about this!! So after another long search, I finally found a calcium citrate supplement at a local health food store. It is by TWINLAB (calcium citrate caps), and the label says,
"No tablet binders, coating or colorings. Free of the most common allergens such as fish, corn, soy, yeast, weat, barley, lactose, and all milk and egg products. No added flavorings, sugars, salt, artificial sweeteners, preservatives or salicylates."
I've been taking them for a few days, and no reactions in dd!! Not the cheapest, but they are working for us so I would recommend trying them out.