I think it's time to give your doctor a call. Here's some information from the drug's website:
Products that contain mesalamine, like Lialda, have been associated with a condition that may be difficult to distinguish from an ulcerative colitis flare-up. Symptoms include cramping, stomach ache, bloody diarrhea, fever, headache, and rash. If you experience any of these symptoms, talk to your doctor immediately. Your doctor may decide to discontinue your medication.http://www.lialda.com/Please don't worry too much if it does turn out to be a reaction. Many of us had to go through a few of this sort of drug before we could find one that worked for us.
Remember, please call your doctor asap. If it's a reaction, you don't need to put up with it: your doctor can help.
Best wishes, and welcome.
Ivy.