Multiple food allergy / intolerance

Hi
I have a strange set of food intolerances, and was wondering if anybody had heard of something similar.

I'm 28 and have Rheumatoid Polyarthritis; I have always had trouble eating fruit.
I appear to be hyper sensitive to anything bitter or acid, and so eating fruit has always been very unpleasant / impossible. The only forms of fruit I appear to be able to eat without getting mouth ulcers and a burnt, white, tongue are cooked apples or pears in small quantities with sugar. I can also eat bananas, and moderate quantities of cooked tomatoes.

In recent years, I've started to develop intolerance to other foods. I either develop mouth/throat ulcers or a white, burnt tongue when I have the following: nuts, certain spices, bitter vegetables (endives...). My most violent reaction is to chili peppers; they now cause a very strong burning sensation on my tongue and red patches on my skin, as well as diarrhea.

I'm worried that the list of foods I react to will continue growing...

Any ideas on the symptoms and possible causes? My grandmother was fruit intolerant, but she got patches on her skin rather than mouth ulcers.

Thanks for your help...