M.R.
This could be sensory processing, but you will probably not get help for this at a pediatricians office. I would suggest that you contact your state and see if you can get a developmental profile done, in Ohio, it is called the Help me Grow program. Most states offer this service. Tell them that your son has been pulling his hair, this is a self injurous behavior (SIB) called triceltelemaina. It could have many causes. If you dont find help from the state, and your pediatricain does not help you with a referal, then look for an evaluation privately. You can start with either an occupational therapist (to evaluate senosry processing) or a Developmental Pediatrican (check with the closest childrens hospital)
Distracting him may be helpful, you will probably have the most sucess with sensory/tactile destractions.
Hope this helps!
M.