Since your UC is left-sided, it likely would be helped by steroid enemas, either hydrocortisone or budesonide. These do not produce the immediate side effects that oral steroids cause. However, the fact that you're middle-aged may be influencing your gastro's desire to avoid steroids & go for immunomodulators. He may be concerned about
steroid's potential for damaging hipbones, etc. I posted reference to a Web article last week that might give you some useful info: New Online IBD Article Summarizes Current Medical Treatment Options-- now on page 4 here.
Did your gastro ever prescribe Colazal for you? It's a 5-ASA that has helped many of us who did not get results from Asacol. The Web article discusses the differences btw the various 5-ASA formulas & has a chart. / Old Hat (nearly 30 yrs with left-sided UC; currently on 3 Colazal daily; seem to be back in remission)