What Causes Headache, Joints Pain And Diarrhea?

My daughter has had what looks like a systemic reaction to poison ivy for two weeks. The rash covered her entire buttocks, much of her legs and arms. She has been on an oral and over-the-counter steroid. In the past several days, I developed a similar, very itchy rash on my buttocks and torso. We are now both experiencing headache, joint pain, fatigue and diarrhea. Seems like it could be something other than poison ivy.