We had a few issues with reactions to fruit (just as you describe) with my eldest daughter.
I spoke to GP about them and he suggested leaving them for 1 months and try again, if there was a reaction, leave off them for another month, providing the reactions did not get worse we could try 3 times before we should go back, mostly the reactions went, it was only melons and cucumber that didn't and she still has reacions now-she is 5.5 now tho so the advice might be different.