My son who is nearly 3, has very abnormal behaviour. he is an incredible memory but loves repetitive actions and isolation?

Worrisome: What you consider an incredible memory I consider a potential problem. Retaining & repeating useless information can be a feature of autism and or intellectual impairment.The drive to self stimulate & avoid interaction with others also fits that pattern.I would have him evaluated by a developmental specialist.

Consultation: Important your child see a Pediatric Specialist with experience in diagnosing and treating children with behavioral disorders, Autism Spectrum disorders, etc. the sooner your child is evaluated the better the prognosis.