Ulcerative Colitis and Stomach Pain

My son is 10 and has Juvenile Arthritis(Spondylitis) and Ulcerative Colitis.  His UC started in Feb with really bad constipation, started him on Myralax which worked nicely. He never had constipation.  Stomach hurt nightly at exactly 9pm.  Thought he was just wanting to stay up:)  Then the diarrhea and blood and clots and coffee grounds started and was put in hospital.  Confirmed for UC in the lower left side of intestines and rectum, which goes hand and hand with his Arthritis.  Was put on 60mg of prednisone, ASACOL 800mg twice a day and CANASA nightly.  His symptoms cleared and was doing well.  Stopped prednisone in May on a tier bases and had to start Remicade in June due to Oriencia(arthritis meds) not working.  All seemed fine until a week ago.  B4 Remicade, always had some traces of mucus in stools, but belly felt good.  After Remicade that went away too.  Last week, Didnt go for 4 days gave him Myralax, after 2 days he went.  last Tuesday started with stomach ache, Remicade treatment last Thursday. Dr said sometimes, a week B4 he Remicade kids feel a bit sick.  OK...but..  Now last night at 9 bad stomach ache again and his bowel movement had lots of mucus.  Bland diet today and still taking CANASA and ASACOL, never stopped these meds.  Why at 9pm everynight his belly hurts BAD.  Afraid the next thing will be blood, clots and coffee grounds....Anything else I can do for him to ease discomfort?  Why starting up when all was calm since March?  Is this just typical, can you get a flair on Asacol and Canasa?