The only way to get relief is hot (as hot as you can stand) water. Run it over the rash.
The heat brings out the histamines and makes it itch like crazy. Hang in there, and keep increasing the temperature of the water. After a while, your supply of histamines will be depleted, and the itching will stop until your body produces enough to make it start itching again (usually 4-6 hours). This will not, I repeat NOT make the rash spread.

Calamine doesn't work.

I am a land surveyor, and see frequent exposure. I used a homeopathic remedy called Oral-Ivy for a couple years...it's actually poison ivy/oak oil extract (urishiol) that you take orally and build up your tolerance. After a couple summers on that stuff, I didn't have to take any more. I'm immune (or close to it - I don't tempt fate) now.

Diggy18, central PA sure has its fair share of ivy, (that's actually where that Oral-Ivy stuff was produced), but the Piedmont of NC is at least five times worse, based upon my unscientific observations. I feel for you.