Unexplained allergy

I am 34 and all my life have only ever been allergic to pollen.  Two years ago out of the blue I experienced severe itching of the mouth and slightly swollen lips when i ate some avocado.  I grew up on avocado so I thought nothing of it.  The same thing happened with banana, kiwi fruit and although I explained it to my doctor, she had never heard of such a thing.  As time has gone on I was able to identify the symptoms immediately and can safely say that I seem to have some sort of reactioin to any kind of raw fruit or vegetable, some giving worse reactions than others.  I met someone else who has a similar fruit allergy but I would love to know what is causing it.  I  have tried organic fruit but it makes no difference.  Any suggestions?  Thanks.