I don’t know if this helps, but my son used to complain of leg pain when he was young.  (He does not have CAH.)  I took him to the dr and they said he had very flat feet and prescribed orthotics.  We went to a therapist who custom makes them and he has worn them ever since - 20 years now and they make a great deal of difference for him.  Coincidentally, my daughter (she has CAH) also had leg pain and it was the same thing.  Recently I went to my orthopaedic dr who treats my arthritis and complained of my ankle hurting and he told me I needed orthotics.  I decided to try the Dr. Scholls before having the custom fitted ones and they have made all the difference in the world.  My point is, it may be something like that causing his pain and not related at all to the CAH.  I’d check it from both perspectives.