postoperative brain surgery

My son is 6yrs old and was diagnosed with craniopharyginoma a couple of months ago and had the tumor removed. He is going through rehab, but now he has constant itching all over his body and there is no breakout and i have to constantly stay on him about biting his bottom lip. He bites his lip constantly and most of the time without knowing, so I want to know if this is a side affect of the surgery?