Well we finally went to see an allergist to figure out what Connor is going on with Connor and all of his food reactions. When I scheduled the appointment over the phone, and had to explain to them why we were coming, she said they would likely do the testing that day so we were ready for it.
After going over his history of reactions to foods, the allergist decided to test him for 10 different foods: egg, cow's milk, soy, wheat, peanut, almond, pecan, walnut, banana, and squash (though it was yellow squash since that was the only one they had). The allergist explained that you have to be first exposed to something to be allergic to it, but that since Connor is breastfed, he has been exposed to the proteins through my milk and therefore we could do the testing on foods that he hadn't actually eaten yet. They did the skin test on his back and it actually wasn't too bad for him.
The results... he is definitely allergic to walnuts and we were given a Rx for an epi pen in case he ever accidentally comes in contact with walnuts. We will retest the walnuts again in a year to see if he maybe outgrows it, but since Ken suspects he is allergic and Ken's sister is also allergic to walnuts, looks like we will be avoiding walnuts in our house and checking labels for tree nuts. We'll also be following up in 6 months as Connor will have eaten more variety of foods and we'll test for more if needed. So as far as immune-response allergy, so far it's just walnuts.
That said, he could still be sensitive to certain foods and need to avoid them (like my non-celiac gluten sensitivity), but it's not something that will show up on an allergy test. So I am to continue like we have been with introducing one food at a time over 3-5 days and taking notes on any reactions that may pop up. This doesn't tell us why he broke out in hives from eating that apple back in November, but hopefully it doesn't happen again. The doctor said she doesn't think it was the actual apple since he eats cooked apples all the time and is fine. Though I have to say, I am still nervous to give him a raw apple again.
I'm glad to at least know that he's not at risk of anaphylaxis with a few of the foods we've been avoiding and maybe just a sensitivity or something he's grown out of. Once we get a few more foods into his rotation of what he can eat, I will be trying nuts he isn't allergic to and a little bit of dairy back in my diet to see if he has any reactions through my milk like he had before. I have to say, I am most looking forward to the possibility of eating peanut butter again! And hopefully Connor won't have any more reactions and it won't be long before he can eat just about anything... except walnuts of course :).