When I got a terrible case of poison ivy, I found a lotion called Zanfel that is over the counter. Although it is expensive, it worked very, very well. It will cut down the amount of time you have to suffer. You put it on the affected areas, wet it and massage it for a short time. Then you rinse it off. The claim is that it lifts the toxin up out of your skin and then it gets rinsed off with the lotion. Of course, it's best if you can use it as soon as you discover that you have poison ivy. There may be other, similar products on the market now. Zanfel was the only product of its kind when I needed something. I highly recommend it.
The duration and severity of a rash from poison ivy/oak is depends on your sensitivity to poison ivy/oak and how deligent your are about not spreading and causing additional irritation from scratching. I'm extremely sensitive and usually have to go to the doctor for a shot of corticosteriod and cream. With treatment, the rash should clear up with in a week. Without treatment, the rash normally lasts on average about 10 days to 3 weeks, but can last as long as 6 weeks for individuals that are sensitive to the plant. Antihistamines and calamine lotion are most commonly used for treatment.