It sounds like you may have the same allergies I recently developed at age 45. I am allergic to tree nuts and stone fruit. If I eat one of those my throat tingles and swells. A fast-acting melt-in-the-mouth Loratadine takes care of the symptoms if I accidentally injest one of those foods. I think this is related to hayfever, which I have had since I was a kid. I have seen this set of symptoms described as "Birch allergy", and being allergic to mellons can be a part of it for some people.
If the fruit is well cooked I can eat it without symptoms. That does not appear to work for nuts.
Unless your symptoms are bad (i.e. going into shock), try eating small amounts of new fruits to see what you can and can't eat. Or get an allergist to do a profile. Once you know what's ok, then you can start shopping wisely and paying attention to labels. You are going to have to get in the practice of reading labels. Learning how to cook if you don't already know would be a big bonus as well.
It's a hassle for sure. It especially bums me out since nectarines are my favorite fruit. My wife makes cooked nectarine desserts sometimes but it's not the same as fresh. It's especially probematic when you do supported century rides. I have to examine all the food for signs of nuts before I touch any. I probably look like a wierdo but there's not much I can do about it. I bring extra food in case I can't eat anything, and I have the Clif bar flavors that I can eat memorized. I also carry some Loratadine in my seat bag just in case. If you have serious symptoms I suggest getting an Epi-pen.