|I'm currently getting over poison oak that sounded like it became as bad as yours - blisters in spots, painful to touch, that sort of thing.
I went to the doctor and she prescibed me oral prednisone, which is an oral steroid. Though it hasn't really helped with the itch, it's really made the rash better. She said what the steroids do is reduce inflamation, which allows the rash to dry up and heal. One reason people are wary of using steroids though is that they have some pretty annoying potential side effects, like increased speediness and jitterness, umm....I've personally had that, as well as some muscle tensions. But then again, if you are not too sesnative to that sort of stuff it may not affect you.
As far as the itching, I don't know if there are any permanent solutions unfortunately. From what I know benedryl is a good one...any sort of anti-histimine. I've been using generic Gold Bond cream, which sort of seems to help, probably mostly because it has menthol, which cools your skin, so you can actually feel an effect. So that temporarily work sfor me. But then again, my boyfriend, who also has poison oak, tried it and said it burned him...I'm guessing it was a reaction to the menthol. So keep that in mind.
Some other temp solutions I've been told are bathing in baking soda or buying oatmeal bath packets, which you can by at pretty much any drug store. The oatmeal is supposed to help soothe the itch. Those too though, are unfortunately only temporary solutions.
Well, I hope you come across something that works for you! Good luck.