I have severe food allergies that just poped up out of no where.?

I am a 19 year old male who just recently discovered that i have severe food allergies to many foods that i never showed a symptom to before. Previousely i knew that i am allergic to nuts (peanuts, walnuts, Almonds, etc) But about 6 months ago i started having random reactions that would send me to the hospital. After those reactions every food seemed to irritate my throat. I do suffer from asthma as well as dust pollin and tree allergies.I finaly had an allergy test with my allergist. I had severe reactions to corn, grean beans, string beans, watermelon, orange, mustard ,soy bean, and sesame seads. I also showed reactions to wheat, barely, oats, rice, white potatoe, sweet potatoes, carrots, oysters, and cod fish and tuna. Up untill those reactions i could eat everything fine and then they just hit me. Where did these come from? Why does all food have to have corn syrup!