I've had it twice. The first time was in California at age 28. I thought I was immune up until that point. It was on the back of my legs for nearly two weeks REALLY bad. I was in the military and the baffled Navy docs finally tried Silvadene cream ( I think it's for burn victims) and it cleared up in a couple of days.
That sounds like poison oak. Seems to be more common out west and I remember a lot of people got it bad when I was out there (California and Arizona) in the Army.