What else to do? PDD/ADHD..

I had my son evaluated just after he turned 4 because of poor speech and some behavioral.
He qualified for Speech, OT (poor grasp), PT (core weakness) and behavioral therapy (biting, hitting, etc)
The neurologist said PDD/ADHD and ordered seizure testing, sleep study and allergy.
Allergies were ok as were the seizure test but he had moderate sleep apnea.
We had his tonsils and adenoids removed by our ENT (the same one that put the ear tubes in at 15 months).
I was hoping some of the behavior might improve but it seems worse. He will be going to a special education kindergarten.

We have an appointment with the neuro psychologist in November right after he turns 5.
I put a call in to the pediatrician and asked if there was anything else we should be testing for.
I guess at this point I'm leaning towards blood work... sugar/gluten allergy or something like that.
I'm waiting for her to call back. Are there any tests I'm missing that could be a physical cause of these issues?

Re: What else to do? PDD/ADHD..

My Dev Ped told me to check iron levels.