I feel sorry that you and your son are having anxiety and pain. At his age it will be tough. Does your son have a sitz bath? The warm water will help soothe the sore and raw tissue inside and out. Sitz baths (or sitz basin) are available at major drugstores or health equipment stores. Also on Amazon for under $15.
Set the basin on the toilet (seat up) and fill it with very, very warm water. Lower into it slowly (some water will displace through the hole in the back and flow down into the toilet so don't worry about the floor getting wet). Your son should sit in the water until it cools. You can refill it with warm water, without getting up, by using the tube and plastic bag that comes with the basin. The warm water will bring a healthy blood supply to the tissues and will help heal the raw and sore areas inside, and around the outside. Dry the skin thoroughly and apply a baby diaper rash cream. I used my sitz basin only a few times after my reversal and never needed to use it again. I remember how soothing the hot water was, and healing. Keep him hydrated with chicken soup, salty clear broths, bone broths, anything to keep his pouchitis-system hydrated. Can he eat solid food? Use a hand blender and turn everything into a hearty thick soup for nourishment as he goes through this. Same goes for you about nourishment. Caregivers need care too. Seventeen years old is so young to have to learn about grit and resilience. Best wishes to you both.