Severe Back Pain

I've been diagnosed with Ulcerative Colitis and have had constant flare ups since November 2009.  When the flare ups start my GI specialist puts me on prednisone at a high dose and every week I taper off along with other meds such as Mezavant.  While on the high dose of prednisone I feel much better but as the dosage decreases the flare up start.  

Recently I was admitted into Hospital with severe abdominal pains and weight loss.  I also started having lower back pain that acts up mostly at night.  The back pain is so bad that I have trouble walking and sleeping. My GI has run all the test (MRI, Catscan, Ultrasound) and found nothing and is not sure if it is related to the UC however when the back pain increases the area of my colitis also flares up.  Does anyone know if this back pain can be associated with the Colitis? Or has anyone had this symptom before?  Any help/advise would be greatly appreciated since I couldn't get any answers from the hospital GI team.

Thank you