Hi, welcome to the forum, anaphylaxis is an emergency allergic reaction and is due to hypersensitivity reaction (type 1). Usually responsible allergen is known.
Drugs like amoxicillin, certain painkillers, certain garments, environmental allergen and certain food (fish, mushroom, peanuts, soy etc) can cause such reaction.
You need to keep track of things (maintain a diary) you were exposed to such as food, cloths, drugs etc. and you should avoid further exposure.