Severe Back Pain after Rt Colon surgery

My husband is really suffering from lower back pain after his surgery a week ago.  He had a mass removed from his colon.  I'm getting worried because no matter how much over the counter pain reliever he takes, it doesn't subside.  The nurse told him he could take Tylenol, Ibuprophen, Aleave, Motrin but no Advil.  He has a few Percoset left from when he checked out but hates to take them because they don't relieve the pain either but make him feel loopy.  What is the cause of this pain?  He has very little pain in his stomach other than when he gets constipated.  But we've pretty much gotten past that.  He h