Self abuse in my 22yo with CP

I have a 22 yo son with CP from newborn grade iv IVH in NICU.  He has cortical blindness, g-tube fed, seizures and is nonverbal and cannot sit/crawl/walk.  Starting around 5 yo he started hitting/punching himself in the face.  This has gone on forever, and he is now 22.  Over the past year, it has gotten way worse and very hard to manage.  He has to have his arm strapped to his wc to ride his bus to his day program, strapped to his bed at night so he does not start hitting himself in the night, and we have to re-direct his behavior A LOT during the day. He always hits himself after he has wet, so we know that is from being uncomfortable.  Sometimes if he has reflux or gets soap in his eyes, he will do it, so it appears to be out of frustration as well.  Or he will just do it to do it.  Dr just put him on 50mg Zoloft to see if that would help.  It has been almost two weeks and I've seen no change.  

Does anyone else have experience with this or anything that has worked for your family.  We are desperate.  Thank you.