I am sorry to hear your son is struggling with the disease. I can tell you it can take time after initial diagnosis to find the right medicine combination. Can you tell us a little more about
his current symptoms.... # of bm's per day, urgency, blood, pain, etc.... Also, has he noticed any improvement from the start of taking medication? Rectal medications would be a good addition to his treatment plan. Also, do you know how far the inflammation extends? You could find that info from the biopsy report.
Another thought is have you tried making any dietary changes. For example dairy and gluten are common aggravators. I suggest keeping a food journal to try and pinpoint possible triggers. Everyone is different so it does take some trial and error. You could also do a search on low residue diet that may help symptoms to improve as well.