It sounds like your son might have some issues with social anxiety that could be treated by a psychologist. Many people struggle with this and feel very isolated, anxious, and lonely because socializing provokes so much nervousness and discomfort that they just opt out. Getting help for your son early will likely help to keep him from going down this path. I would suggest finding a psychologist who specializes in working with school-age children. Therapy might feel awkward to your son at first, particularly given his anxiety, but a good child psychologist will be able to help him feel more at ease within a session or two.