I suggest you report this to the doctor who is treating him so he can make
adjustmentsAdjustment disorder in the dose. Different doses do have unpredictable effects, and more is not necessarily better. You might also ask this question on the child behavior forum here at medhelp, they deal with these kind of issues more than I do and may have more specific advice to give you.
It's not uncommon for folks with AD(H)D to have what's called the 'rebound effect' where the symptoms return as the medication wears off -- it's unclear whether this is subjective (just seems worse because they were so much better on the stims) or an actual biochemical thing.
Try posting your question at the ADD Forum on www.about.com (run a search for ADD once you're there and the ADD page with forum will come up) --many folks there with lots of experience with this.
Helen