I've had severe allergic reations to something an allergist nor my reg. dr. can'figure out. I carry an epipen?

I've had all the scratch tests. There is no rhyme or reason when this may occur. Throat closes up, severe swelling in hands and I turn bright red, my tongue swells and my voice changes. It's very scary.One allergist said possibly a virus. After one episode it was almost a year later before another. I then had three in one day and I fainted with that one. I don't know where to turn as everyone seems to be baffled. Please respond.