Allergies - How do you know & what do you do? Help!

I get a sore mouth when I eat raw tomato. its ok after a wash though

Hmmm, we've not given him Kiwi yet, I wonder if that will be the same? Strawberries he tried in the summer but wasn't really 'eating' eating at that point iykwim? So he mouthed them but didn't mush them to the extent that any juice went on his skin.

Thanks ladies, this is all very helpful