This thread is old, please check the date in future posts as the original posters might not be here anymore to answer your questions
In my opinion, two theories :
1/ you said it was in a facial soap and in a body product. Maybe the reaction is not due to shea butter, but to other ingredients, or the whole recipe. Maybe check the ingredients list on both these products and see if there's any common ingredient. Do you have any other known skin allergy issue with a certain product/ingredient ? I know it's easier said than done but it might help you prevent future allergies.
2/ you are allergic to shea butter. It is totally possible, we sometimes assume because something is natural it's safe for us. We tend to forget most of our products are just chemically produced versions of natural supplies. Besides, belladonna is natural too, yet it is poisonous.
You're not allergic to nuts, but the allergy process is not entirely mastered by modern medicine, i know some bizarre associations exist that if you're allergic to something, you should avoid another. I also know for a fact food allergies can build overtime and be started by environmental factors.
To be sure, i'd do a patch test, say in your elbow, with pure shea butter. If you're allergic it should provoke a reaction quickly. Ask around, maybe one of your relatives has some.
The other possibility is go to a doctor and ask for an allergy test.
If you are allergic to shea butter, go for other butters, i think the easiest to find are cocoa and mango butters. You may have to get the pure butters, as i think the most widely use butter in skincare remains shea.