We put our son on Adderall XR when he was 5 also. The first night he was on it, he built a stack of blocks, which he'd never done without getting distracted. So we though "OMG! Look at that! This stuff really is helping him!!". So we ignored the signs that slowly appeared over the next few months - he stopped eating and sleeping (had to put him on Remeron to counteract that), he started getting tics (he now has full blown Tourettes), be became very aggressive and mean (where before he was the sweetest kid ever), and when he wasn't aggressive and mean, he was like a zombie. But he WAS able to sit still in his pre-school class, so the docs were still pushing the Adderall.
Finally, one day, the doc decided that my son had anxiety in addition to all his other stuff and wanted to put him on Paxil. Poor 5 yr old kid was on Adderall, Zyrtec (for his allergies, and which, I suspect contributed to the aggressiveness), and Remeron, and NOW the doc wanted to put him on Paxil. I'd finally had enough and took him off the meds and changed doctors - this protocol just wasn't working.
A few days after we took him off Adderall, his pre-school teachers were SHOCKED when my son smiled and laughed - they'd never seen him do that. And even I realized that I hadn't seen my son happy for almost a year. The Adderall had completely wiped out his fun, happy, sweet personality and replaced it with a mean, and aggressive, or totally zoned out, kid.
Now it's many years later, my son is now 15. He takes Intuniv, which he's been on since he was 6 (it used to be Tenex, Intuniv is the extended release form). It's a much better fit for him. It helps him concentrate, but doesn't take away his personality.
If you find something isn't working, there are many medications out there which might be a better fit. Unfortunately with ADHD, what works well for one won't necessarily work well for another. It's trial and error. And sometimes, when something DOES work, after a while, it stops working. It's just the way it is. I think we got lucky with the Tenex/Intuniv. It works for my son and there are NO side effects that we've noticed. We tried Strattera a couple of years ago (on the recommendation of his doc) and it was a disaster (like the Adderall). So for now, we stick with the Intuniv
I hope you find what works for your son.