There is an interesting anecdote attached to this one. One summer, we found a mysterious and attractive wildflower out back of my bf's mom's house. Later the same summer, I contracted a horrific case of poison ivy.
Close to three weeks of scratching, squirming, Calamine-encrusted misery ensued. During a heatwave, no less. I tried everything available over the counter to no avail.
Reading up on wildflowers out of simple curiousity - I fortuitously discovered this plant I'd been curious about was called Jewelweed, or Spotted Touch- Me-Not. The field guide I was reading metioned that it's considred an excellent treatment for poison ivy. Right in our own backyard!
After doing some research on how to prepare the stuff for use, I found the following instructions at www.altnature.com. It worked within a couple of days after everything else had failed. That it could be frozen as ice cubes had added benefits on a really hot day. Best of luck with this and please let me know if it works for you, too. : )