I don't think it's weird at all that you are allergic to Asacol and Lialda, as they both contain mesalamine as the active ingredient. It is odd, though, that you had the exact same reaction to imuran. I have no idea what might be causing it.
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, Culturelle probiotic, and Zoloft (25 mg).