D.B.
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First of all, a little bit of admin advice. You have very little info here, so we'll all just be guessing. If you want to expand your question, please click on "edit" and write "added" or "ETA" (Edited to add) and write more. Please don't actually answer in the same section where everyone else will be replying - not every responder will see that as being from you, the original poster. And FYI your question posted twice (not your fault - probably the server was slow to upload so you understandably clicked twice and it posted twice). But, that means you will get answers on either of the posts, and not all the responders will see the other answers nor any updates you make. You can't delete your duplicate but you can edit it to remove the content and perhaps just write "duplicate - removed" to explain.
Anyway, I'm surprised that your child got to age 12 without any teacher or pediatrician talking about this or asking about his social skills, how he deals with crowds/noise and so on. It's unwise to jump at one condition such as autism (or anything on the spectrum) - please raise your concerns with the professionals who know and observe your child. There are many moms on this site who may suggest specific questions to ask or evaluations you can request, and of course you must advocate for your child. But do ask for evaluations that cover a variety of things and don't assume that he has autism.
At 12, kids often become hormonal and insecure, so you have to factor that in. It's also important to have the professionals investigate whether any form of trauma has occurred that could prompt a change in behavior.
You say he has exhibited symptoms since he was younger, and I'm concerned that no teacher ever requested that the school psychologist or other professional come in to observe him. I think you may have to push hard to get the school to take this seriously. So do find out what intervention and testing/evaluating services are available to you.