What Causes Itchy Hives With Pain?

I used to break out in small itchy hives after sex. I was using condoms at the time and thought that the latex was irritating my skin. Once I stopped using condoms the breakouts stopped for a while. However, I still break out every now and again if I haven't had sex for a little bit. They are itchy and sometimes they hurt. They don't last more than a day or so, but still it's uncomfortable. I have been checked for stds and I am clean so that isn't the problem. Is this normal and is there anything I can do to prevent it.