My 5 Year Old Had Is Tonsils Out Friday. His

My 5 year old had is tonsils out Friday. His recovery has been amazing, until Sunday night. He started complaint of his cheeks hurting. We have done icepacks and it doesn't seem to phase it. For 2 days now we have been dealing with it. This evening I d coded to make him let me look in his jaws and there are blister/ulcers on them. I have been catching him kind of chewing on them from time to time. His eating and drinking has slowed way down compared to the first 4 days. I have been doing lortab and rotating with ibuprofen as prescribed. But the pain meds does not help with his "cheek pain." Now he screams when giving meds bc it burns the sores. What can I do to make him him more comfortable? And could all the medicine he is taking have caused those. I just figured the lortab was making him "naw on his cheeks." When I see him do it I remind him to stop. He is also on antibiotics. His throat doesn't bother him at all it's his raw cheeks rubbing his teeth every time he talks, eats and drinks. Please help!