I am allergic to wheat oats barley and rye. I am celiac.
I have a friend who has gone through a terrible time with rashes and she knew she was allergic to fish and corn and wheat. She just found out she is allergic to yeast.
I hope you find out the source of your reaction. If you call the maker of the cake they should tell you what the ingredients were so that you can track it down.
Good luck.
Rita