Here's my $.02 based on my own experience.
You may remember that several years ago I took a really bad tumble down my basement steps, resulting in hellacious swelling and bruising that lasted about 6
months. My backside looked like a purple J Lo on one side, and a purple me on the other.
A few days later I started getting hives at the site of the impact - on my sacrum. I thought it was cold urticaria from ice, so I stopped icing it, but the hives continued and spread all over my body. After several weeks of this I went to my allergist who did a full blood panel to rule out anything scary (like liver disease, leukemia, etc.) and informed me that my immune system had turned on to attack the injury and was running amok. Generally if the hives don't go away within about 6 weeks, you're stuck with them for life.
And so far I am. They're not as bad, and I can skip my Claritin for a day or so here and there. But if I skip it for too many days they come roaring back. Yep, I'm on Claritin for life.
Now, for the life of me I can't remember if my allergies were any worse than usual at that time. It was November, so they would have been on the wane.
I have also seen younger DS react to cooked fruit when he was sick, when he normally only reacts to raw fruit.