Prednisone is the most likely suspect, in my mind.
If that is the cause then it is really easy to test, start taking a small dose of predisone for a few days and then tapper again.
DX'd with Severe Pancolitis June 2005
Previous Meds: 5ASAs, Predisone, 6-MP. Remicade, Humira, Simponi, Cyclosporine -- Twice
3-step J-Pouch surgery: 2013 & 2014
Current Condition: Chronic Pouchitis -- Not as bad as I thought it would be
Current Meds: Cimzia and Sulfasalazine