I'm bumping this thread to keep the ideas coming. I've been battling phoning hives something fierce this last week and trying to find answers.
Mid-March, same time frame as your last complaint in 2012.
Tax season? Seriously though, I broke out in hives one semester in college when I took 21 hours, had a job, officer in a club, and had a girlfriend. Stress was the cause. After that semester, never had em again. Broke out in shingles ( lousy with chickenpox as a child ) during the election of 2008. Stress again.