I'm allergic to something and I don't know what it is

A long time ago, I went to a new restaurant with my family. The restaurant was really fancy and the food was great. Afterwords we went to a movie. About half way through the movie my arm started itching. When we got home I had a huge red blotch on my arm. The next morning I had a lot more all over. I didn't know what the ingredients were (of course), so therefore I don't know what I'm allergic to.