I'm only on Apriso and mesalamine enemas (twice weekly for maintenance) and have been in remission for close to 2.5 years now. Has your doctor brought up other meds, such as 6MP, Imuran, or Remicade? There are several people with UC who can't maintain remission on mesalamine drugs, but do very well on others. It really sounds like mesalamine drugs aren't going to work well enough for you.
Status: Remission since May 2009!
Symptoms began in November 2008, ~4 weeks after giving birth to my son
Diagnosed with pancolitis on 1/30/09
Meds: Apriso (4 0.375g pills ONCE!! daily), mesalamine enema twice weekly, Natural Factors Ultimate probiotic 12/12 Formula, multivitamin. Used prednisone (starting dose 40 mg) to get into remission.