Please help..

I am a single 49 year old father of a two year nine month old boy. He has some very peculiar traits and I'm hoping that maybe someone can help me. 

He is:

1. Very intelligent. The smartest child that I have ever come across and he is routinely acknowledged by strangers as being extremely intelligent

2. His vocabulary is enormous. Far beyond children much older than him. He has been talking non stop forever. 

3. He is and always has been extremely social and friendly.

What he does:

1. Repeats things over and over and over and over again. Seems pathological.

2. Fixates on one thing. He's been on Cows for months. As I sit here he is repeating "Lets make gravy, lets make gravy".

3. The repeating seems to get worse the more that he is tired.

4. He holds his hands in a stiff way all the time. He bends his wrists in and holds his fingers straight.

5. He doesn't always like to make eye contact .

6. He doesn't like to be touched and doesn't like blankets on him.

7. He doesn't respond to pain in a normal way. He doesn't cry when he gets hurt. He never has.

8. He will hit his head against things on purpose or jump up and land on his knees in anger.

9. He lines up his toys or stacks them.

10. He really never quits talking. If he is awake he is talking and demanding attention. .

Does any of this make sense to anyone? Am I asking the right question in the right place? I really need help here.