Hello and hope you are doing well.
Normally, during the course of evolution from a baby to an adult, we develop a mechanism by which we desensitize ourselves to all the materials we are exposed to. But sometimes, the desensitization may not be perfect and we develop allergic reactions to those few substances. This is what happened in your case. On exposure to the allergen, an Immunologic (IgE) or a non-immunologic reaction is set in process, which ultimately releases histamine, which acts at the peripheral receptors, resulting in allergic reactions, which can range from rashes to anaphylaxis.
The aim of the therapy is identification and removal of trigger factor. It is the most important and the only effective long-term therapy. To prevent the allergic reaction, the allergen needs to be avoided. It may help to maintain a food dairy and keep monitoring your symptoms. This will help to narrow the search and avoid them. Further allergic testing may be worth looking into.
Antihistamines block the histamine receptors and prevent histamine from acting and thus help with symptoms.
Hope this helped and do keep us posted.