I live in Poison Oak Terror-itory.
And old Cowboy we use to trade eggs with for goats milk helped me for life with this advice:
Monty said to get a bar of Ivory Soap (99 44/100ths percent pure) and wrap in in a clean white wash cloth.
Get in the shower and turn it up as warm as you can stand it, scrub anywhere it itches.
Then turn up the heat as much as you can stand it and repeat.
Do that until you get relief from the itching.
In a few hours, or when it starts itching again, repeat.
Monty's method worked wonders. Dryed it up in a matter of a couple to a few days.
I've have had Poison Oak so bad it was on the inside as well. Monty's technique worked every time.

Also, take anti-histamines, like Benadryl, to help fight the discomfort from the inside out.

The heat of the water brings the oils to the surface, and the soapy wash cloth cuts it loose so it goes down the drain.
He also warned against using other soaps. Some deodorant soaps make it worse.

And I bet you have a bar somewhere around your house right now.
(Ever wonder what the .66% is?)
(Kind of like Maxwell house coffee. Good to the last drop! What is wrong with the last drop?)