Have you gotten him checked out for autism spectrum disorders? From the small amount of information you've given, my first thought was "Asberger's Syndrome," which often shows itself in very bright/smart children that have major behavior issues (and often bad allergies, too!).
If you are looking for a Pediatric Neurologist, you should find one that specializes in Autism Spectrum Disorders. However, Developmental Pediatrians, Childhood Psychiatrists and Childhood Psychologists can also diagnose. But please make sure that whomever you choose does work with autistic kids. I'm not a professional in any way, but I'm just going on the info presented.
Here are a couple I found on the Autism Speaks website (GREAT resource!):
Dr. Valerie Nowinski, Pediatric Neuropsychology, Early Childhood Autism Initiative. Our office specializes in early identification and treatment: early childhood programs brain training. This place does not do any insurance directly, so you'd have to submit claims to your own insurance for reimbursement (instead of the Dr doing it on your behalf).
Contact Name: Dr. Valerie Nowinski
Contact Email: ____@____.com
http://www.ndcbrain.com
Neuropsychology Diagnostic Center for Autism and Related Disorders
Century Medical Park
16001 South 108th Ave.
Orland Park, IL 60467
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Neurohealth Associates is a unique Chicago-area practice that capitalizes on our expertise in the areas of neuroscience, neurofeedback, neuropsychology, biofeedback, cognitive therapies, and behavioral neurology. Their website says "Major Insurance Accepted"
http://www.nhahealth.com
Neurohealth Associates
477 East Butterfield Road Suite 408
Lombard, IL 60148
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If it does end up being Austism Spectrum, I've heard great things about this place (and it's close to Naperville!):
Giant Steps Illinois, Inc., and its sister organization The Autism Training Center, Inc., strive to improve a child's ability to interact, communicate, and develop academic and daily living skills through a one-on-one integrated holistic approach of services: speech/communication therapy, occupational therapy, music therapy, social work and educational programs.
Contact Name: Bridget O' Connor
Contact Email: ____@____.com
http://www.giantstepsillinois.org
Giant Steps Illinois, Inc
2500 Cabot Drive
Lisle, IL 60532
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Good luck to you and I hope you find the answers you're looking for!