So are they assuming the itching and bumps are due to the Asacol, and that's why they are taking you off of it? Azathrioprine is a maintenance drug, but it takes a few weeks to start working, which is why you'll be on the prednisone at the same time. I would request to have blood work done before starting the aza.
www.ccfa.org has a lot of good info about the medications used to treat UC. I'd go there and do some reading to learn more about your medication options.
If you want to stay on the Asacol a while longer and see if the itchiness goes away, you have every right to do so. Just talk things over with your doctor.
Symptoms began in November 2008, ~4 weeks after giving birth to my son.
Eased for ~3 weeks in December, possibly b/c of probiotic use?
Returned in January 2009 (with a vengeance), diagnosed with pancolitis on January 30.
Currently taking Asacol (400mg 4 pills 3x daily), Rowasa nightly,
40mg 30mg 20mg 15mg 10mg of Prednisone (quick taper), Culturelle probiotic, and Zoloft (25 mg).