Maybe you are allergic to something. There is no reason to get hives while waiting to see if you have conceived.
I am experiencing it right now for the past 5 days and I'm 10dpo. I'm also autoimmune. With my first pregnancy with my son I developed pupp (can't remember I there's another p!) and so I think it's possible. Anything can happen. I'm not looking too far into it- I just know its strange and annoying. This is the first time this has happened in 2 years since TTC and I've not changed anything I use- we mainly use dye and allergen free items anyway. Btw I know this post is old, but just wanted to share!