Why would lettuce, peanuts, bananas, etc., make me nauseated?

For years I have had extreme nausea (feels like the flu) after eating iceberg lettuce (some symptoms with romain, etc., but not as bad).  Lettuce was the only thing that made me sick this way, when I was younger, but now, as I have gotten older (now 48) I still get terribly nauseated if I eat lettuce and can no longer eat bananas, peanuts, almonds, eggs, green peppers, or peanut butter without getting nauseated.  I have been tested through the years for gall bladder and stomach problems, but nothing was ever found or reason given for this problem, other than an irritated stomach lining.  I do take medication daily for acid reflux, which started during pregnancy and has been an issue every since.  Other than that, no other problems.  

Also, my 20 year old daughter has the same reaction to lettuce, which started as a teen!

Any idea what might be causing this problem for us?