Suggest Treatment For Ulcerative Colitis

I have had ulcerative colitis for over 20 years. Up until the past year, my flare ups have been once or twice a year and responded well to asacol. Since I can no longer get that, the time released asacol has not been as effective. Today I started azithioprine with breakfast and after dinner this evening I had the diarrhea. I know this can be a side effect, esp. Taken with the mesalamine. I will call my doc tomorrow but wondering if I should take the azithioprine with breakfast in the morning. I am also still on 10 mg of prednisone trying to clear up the colitis. YYYY@YYYY