I am WAY late chiming in, but I wanted to do so, anyway. I SOOOOOO feel your pain!
My son will be 10 in May. He's a great kid in most ways, but his ADHD (which is fairly mild, and therefor unmedicated) has been ticking up in the last few months. Every change in routine sets him off. Christmas less than 2 months away? Ooo! Get hyper! Sister's birthday Friday? Hyper! TV program he wants to watch next week? More hyper! Seriously, dude? LOL
There is also a new attiude aspect to the whole thing that is making life difficult. He had to deal with a bully during basketball this season, and that threw him off a LOT. His mother (he's my step, but I just consider him mine) went a bit overboard on trying to stop the bullying, so now he has taken to being a bit of a bully himself, getting in trouble at school for picking on other kids kind of thing.
I've also found that my son gets spacy in the couple of days before he goes to his mom's, as well as the days after he gets back. So I only seem to get about 10 out of 14 days in a row before he seems to lose his mind. *sigh* LOL
The only thing that seems to help is repatition. "We'll talk about that later; sit down and work." Said about 30 times in an hour.
I know you're certain it's not food, but what is he eating at his dad's? My son gets Hamburger Helper, boxed mac and cheese, potato chips and fast food all weekend when he's with his mom. To balance him out a bit, I have to avoid nearly ALL processed foods. Other than bread (which costs an arm and a leg to avoid the preservatives!), if I don't chop it, bread it, make it scratch, I don't feed it to him unless I want some sort of spaz for a day or two. One day he came home after having pancakes with syrup PLUS sugary cereal for breakfast, a bunch of red Halloween candy and a supper of Kraft Easy Mac. I swear the kid vibrated for three days!
The attitude has also really kicked up around here recently. He talks back to his mother all the time, which is irritating, but not my problem when it doesn't happen in front of me. She gives in to his every whim and then just can't understand why he tries to walk all over her. And, since it works so well there, he's started bringing that attitude home with him. Fun!
Some of it is an age, I think. They're starting to pull away from us "uncool parent people," which is what does eventually have to happen. I have fought back by trying to never put him in a position to fight me. The word "okay" is a magic word with my kids. If I give an order but tack "okay?" on the end, it gives the illusion of them having more control and more choice.
"J, feed the dog now, okay?"
"I want to finish this [video game/drawing/whatever]."
"But the dog needs food now. Go quickly and then you can finish that, okay?"
"Okay" (sometimes an agreeable okay, sometimes a grumpy one, but they tend to get moving once they say okay back).
I also try to break up the orders and tasks more for him on days when he is having a harder time focusing.
"J, make your bed, okay."
Bed made.
"Pick up your Legos."
Legos up.
"The clothing needs to be in the hamper, not on the floor."
Ta-da! Clean room. Yes, I probably had to send him back to the Legos twice and point out the socks sitting on his toy shelf (?!), but at least we didn't fight over it.
We have cue words to help him stay focused, too. If he's doing a worksheet and starts staring off into space and shaking his pencil, I walk by and tap the paper gently. For math, which is difficult for him, I make time to sit down and work the problems beside him, then compare answers. The "race" to finish each problem syphons off enough of his energy to keep him working, most of the time.
I'm ADHD myself, so I can understand it better than his dad. I've had to teach my husband some of the skills my mom used to try to keep me focused.
Parenting a high energy kid is hard work! There are a lot of good books out there on coping, though, and you and your son could really benefit from hunting for them at the library. What we hyper kids lack in focus and discipline, we make up for in creativity, energy and a sense of fun! It's up to you to help him learn to use that for good instead of ornery, and it sounds like you're determined to do that! Lucky son you have, to have a mom like you!