Feel a bit daft posting this but I am trying ds with potato. He is allergic to cashews and egg, has been tested for a load of other stuff but all came back negative. Whenever I ate potato or tomato (he's breastfed) he would suffer with stomach pain and produce a green mucousy nappy after which he was fine again. The last time I ate cherry tomato - about 3 months ago I think - the skin on his bottom was bleeding when I changed him 
. It was fine by the next nappy change. I should add, I eat a chinese meal with okay sauce (based on tomato puree) every friday and that has no effect on him at all. Other than that I avoid tomato and potatoes.
We saw Adam Fox last month who said it was quite common for this to happen, but for the child to be fine when they eat it themselves. So far I've managed with giving a variety of fruit and veg as well as dairy and wheat, but i know I've got to branch out a bit and start giving something more like proper meals, but I'm so nervous about giving potato!
So far, I've rubbed a bit on the back of his neck, and put a tiny bit the size of about half a grain of rice on his tongue with no reaction but now I've got to try a bigger bit. He has had a tiny dose of cetirizine this morning - which Dr Fox said would not mask, but lessen, any reaction - but I would know by now if he was going to react, wouldn't I?