Prince, you should get a referral to see a child psychologist or a developmental pediatrician (a kids' doc who specializes in how kids grow up and how their brains' develop).  There are some tests the doctors will give your child to see if they are autistic (aka "on the spectrum"), add/adhd, or some combination. 

Some signs that you should be concerned about: 

Does your son flap his hands or stand up on his tip-toes?  Is your son verbal -- does he speak, if so, does the way he speak sound like the way other kids' speak?  For example, does he talk in a monotone?

Does he make eye contact?

Does he respond to you when you call him by name and look at you in the face?

Does he have particular, overwhelming interests that he talks about incessantly (pokemon, looking at spinning wheels, Thomas the Train)?

Can your son express emotion either verbally or physically (like hugging you or being hugged) without getting upset?

Does your son have rages that are uncontrollable?