Interesting, I can find no mention of a 32mg dose of concerta. Is he on a 36 mg dose? if he is, "The maximum dosage of Concerta should not be greater than 0.9 mg per pound of body weight."
fish oil is certainly something worth trying. There are ones out there developed specifically for kids (chewable, etc), and they will have the suggested dosage on the bottle.
I really can't see any reason that primrose (I assume the oil) would be worth your money. If he is having sleeping problems, his doctor needs to be aware of this.
by the way, there is a whole forum dedicated to ADHD found here - http://www.medhelp.org/forums/ADD---ADHD/show/175
and I would be glad to answer any other questions you might have about ways to help your son. Supplements are only one part of the way to help.