Poison oak which is just about the same as poison ivy (AFAIK) can be relieved but this methods is radical. I don't catch either myself but kids did. This is what we finally discovered, but it is a rather severe method, so use at your own risk!
Strip to underclothes, sit on a sheet, and get some salt, a little coarse is good. Rub the affected areas with the salt. It relieves itching (in a way) and breaks open the rash. Stings, too. Speeds up the healing process very fast. But, as you can see, it is when everything else including patience, fails.
My kids said it helped a lot. We tried everything else, and nothing worked.
When you get in the shower and know you have been in it wash with bleach...I know I know but it works.