Poor kid. I thought you needed to be off Claritin for more than 48 hours in order to get a good skin test. I haven't tested anyone in my family for a while, but it seems like they told me the newer drugs needed a longer wait. That may have just been our allergist, he is really conservative. My daughter has had reactions like that, but nothing long term. We keep finding out weird things that trigger it--aloe is the newest culprit. I still have flare ups, as does my husband so we are pretty aware of this problem, but it is tough to narrow down. Good luck. You are on the right track with the allergists. Be sure to take the pictures with you. Do you have a lotion that you can use (I like cetaphil)? If so put it on him when he comes out of the water. At least in my experience that helps.
MA