Nothing more frustrating than seeing that rash grow and grow....
There are many ways that a rash can spread and a very prevalent cause is reinfection. Washing under the fingernails is very important after having come in contact with poison ivy or one of its cousins. I also understand that a rash can spread from scratching. That's right - scratching releases histamines to the skin which causes a rash. Already got a rash? Well, you can get some more.
Read my message with some great links about scratching:
Don't stress over that rash
So after making sure that you have done everything possible to make sure that there is no urushiol oil left to contaminate you, look to ways that histamines could be produced by your body. Stop that scratching!