3 days after my 13 year old son has been diagnosed

I'd give him some time to let it sink in and as suggested get some books about ASD, there are books out there written by people on the spectrum themselves(or relatives of them) which personally I think are better reading then a professionals clinical view of things. Particularly because he's so young, you may want to find something more age appropriate that he can read himself without possibly being confused by certain terms or 'large words'.

Just from a quick search on amazon I found these;

http://www.amazon.co.uk/Can-Tell-About-Asperger-Syndrome/dp/1843102064/ref=sr_1_4?s=books&ie=UTF8&qid=1343826837&sr=1-4

http://www.amazon.co.uk/All-Cats-Have-Aspergers-Syndrome/dp/1843104814/ref=sr_1_5?s=books&ie=UTF8&qid=1343826837&sr=1-5

http://www.amazon.co.uk/Special-Book-About-Diagnosed-Diagnosis/dp/1843106558/ref=sr_1_5?s=books&ie=UTF8&qid=1343827103&sr=1-5

http://www.amazon.co.uk/Blue-Bottle-Mystery-Adventure-Adventures/dp/1853029785/ref=pd_cp_b_0

http://www.amazon.co.uk/Mice-Aliens-Asperger-Adventure-Adventures/dp/184310007X/ref=sr_1_6?s=books&ie=UTF8&qid=1343827156&sr=1-6

Also this documentary I saw on newsround a few months back was quite good at explaining things for a younger audience;

http://www.youtube.com/watch?v=ejpWWP1HNGQ

Or try Tony Attwood's website which is http://www.tonyattwood.com.au/ if I've got it right or just search Tony Attwood. The website has a section "about aspergers" which is nicely calmly written to explain things without making anyone feel uncomfortable.

There's a nice expression that people sometimes use when describing aspergers - "there's nothing wrong with me - its everyone else that's the problem".

This is true to an extent. Aspergers affects social communication/interaction and therefore is picked up on by other people who find the person with asperger's different or out-of-step (or maybe slightly rude, or inappropriate, or tactless, or moody/morose.....or a number of perceptions that usually other people aren't sure about.

The problem lies with the social communication/sensory/organisational and other difficulties caused by having aspergers. But the problem is other people reacting to this. Most people with aspergers don't feel that they are necessarily the ones with the problem.

That's not selfishness (or lack of empathy as is sometimes suggested). But people with aspergers are usually trying their best to fit in but getting seemingly unfair reactions and maltreatment they cannot comprehend.

So he may not feel that putting the problem down to him is fair. He may feel other people ought to try to be more accommodating.  Admittedly someone with aspergers could be seen as very difficult or uncooperative. But it is due to factors they cannot easily alter.

Try not to make it seem like the label means it is all down to him. Because there's not a lot he can do about it.

If he's been diagnosed with Asperger's, buy Tony Attwood's http://www.amazon.co.uk/The-Complete-Guide-Aspergers-Syndrome/dp/1843106698/ref=tmm_pap_title_0

And just leave it lying around the house, somewhere where he'll see it.

And if he's not been diagnosed with Asperger's, I'm sure there are other similar books one could get.

And, don't try to force him to talk about it.

We, on the spectrum, often process emotion very differently to neurotypicals - rather than talking about it, or 'externalising', we 'internalise'.

So, his reaction is fine, and normal, for someone on the spectrum.

Also, does he have free access to the internet?

He may well, in time, seek more information by himself.

Give him the time, and the where-with-all to do so, unpressured, and on his own terms.