Is it possible to be allergic to everything? I seem to be developing allergies to several different foods amongst other things.

Food allergy. Although rare, some people are allergic to so many foods that avoidance is extremely difficult. Unfortunately, some persons are told they are allergic to a food solely on the basis of an allergy test (typically a rast). A rast detects allergic antibody (ige) however; a positive rast does not diagnose food allergy. If you can eat a rast (+) food without allergic symptoms, then you are not allergic.
No. There are so many things to become allergic to, that it may seem you are allergic to everything. But the way to find out what you are truly allergic to is to get tested by an allergist. Once you have that information, you and you doctor can work out a plan for how to best avoid or handle your allergies.