Your son has many classic signs of ADHD. Doesn't mean that is what he has, but it certainly is worth looking at. I will give you a good site to check out a bit later.
The anxiety, frustration, anger are typical of someone who has ADHD, and doesn't know or understand why people are always on their case. As a school principal I would watch kids on the playground hit, slap, push other children and when asked about it - really (honestly) weren't aware they had done it. This kids were ADHD who reacted without thinking (no filters). Typically, they had one or two close friends and the rest of the kids stayed away from them.
It sounds like your son is quite intelligent. Intelligent kids with ADHD can go a ways through school before they start to have problems. I have found that its about 4th grade and usually math that they start to have problems. And, of course, there are some kids who are so smart that they literally can coast all the way through till college. Anyway, I would have a talk with his teachers to see if he shows any of the classic symptoms. Last year's teachers might be a better place to start since they would have had more time with him. I have several good sites for ADHD information, but I would start here - http://www.help4adhd.org/en/about/what/WWK1. This will give you a pretty good list of symptoms.
I am also the CL on the ADHD website here -
http://www.medhelp.org/forums/ADD---ADHD/show/175 and if you want more information or have other questions you can easily reach me there.
And I think that if this information does sound possible to you - it might be a good idea to ask your pediatrician for a referral to either a psychologist or psychiatrist who specializes in ADHD so you can get the best help.
A quick comment on your question about a months punishment being harsh. Punishment is usually done as a way to change behavior. For someones behavior to change the way to do it is with immediate and age appropriate action. And, of course, consistency is also very important.
While a months punishment might work for a child in high school, it really is not effective for a child of this age. Not only that - what if he screws up again? What are you going to do? Put him on bread and water?
But more importantly, if he does have ADHD this form or behavioral change will never work - and will probably make things worse. Kids with ADHD need behavioral change. It is as important or more important then medication. If you do think he might have ADHD, I suggest you get the book - "The ADD/ ADHD Answer book," by Susan Ashley. She has lots of good ways to change behavior as well as ways to help in school etc. Another good book is Love and Logic by Fay and Cline for behavioral change - although you would have to tweak it a bit if he does have ADHD.
And by the way, I get the sense that both you and your husband are frustrated by whats going on and that is beginning to effect your decisions. So its definitely time to get some answers!!!!
I will monitor both this site and the ADHD site if you have any more questions. Best wishes.