I can only assume that too many antihistamines will dry out the skin, because they do dehydrate the body. One thing to keep in mind is that using the antihistamines too much will also cause one to develop resistance to the medications so that they are no longer as effective as they once more, so you end up having to use more and more and more.
As one who has Multiple Chemical Sensitivity, you have my sympathy about the urticaria
You should be careful about the Calamine lotion, because you are dealing with a lifelong illness, as am I. You could develop resistance to the very pharmaceuticals that you need. Then you wouldn't have anything to use for when the symptoms are at their worst.
I'm also surprised you're even able to function during the day at all. Zyrtec is just about as sedating to me as Benadryl is. I think you have already developed some resistance to the antihistamines.
It is actually important to take breaks from taking antihistamines to reduce the level of resistance to the medications, so that you will still have options to use to deal with your life long illness. I know it is sort of auto-immune, because I have a neighbor with urticaria
, and I've read many posts about it. The most similar thing I have is eczema, which is also a life long condition that I have to be mindful of or suffer the consequences. So, yeah, I understand that you're trying desperately to stop the maddening itch and the outward flare ups.