The allergy to alcohol or to coke even can be due to preservatives, coloring agents, yeast used for brewing, sulfites, gluten products in the
alcohol or even to grapes and other bases. You need to go for an
allergy testing for the ingredients of the beverage you take to know what you are allergic to. It is difficult to comment beyond this at this stage. Please let me know if there is any thing else and do keep me posted. Take care!