I am so frustrated

Hi - I have a son who will turn 5 in a week. I did not notice anything off about him until he was about 18 mo old. He just did not like being in crowded places and was slow to talk. Just as I was about to take him to be DX'd, his language and social skills increased quite a bit.

He started preschool when he was 3 and was very quiet. He flaps and hums when he is excited, doing a lot of physical activity or is stressed out. The flapping and humming are one of my main areas of concern.

He also has a lot of difficulty answering who,what, where and why questions. I put him through our local child find program where he scored very low cognitively, even though I know he is smart. They put him in OT, language and has an inclusion teacher come once a week to his school. All have said the cognitive scoring was a result of his inability to answer questions well. He just wouldn't answer so he zeroed.

I have read autism, SID and PDD NOS checklists a thousand times and I just don't know what to think. His pediatrician tells me he is too social and talkative now to be autistic. He has several friends at school. He talks w/ them, not just parallel play. He knows all of his letters and numbers and can count past 25. I will say that teaching him his letters has required a lot of effort on my part - flashcards etc... He used to do repetitive speech but has stopped that.

He likes wheeled cars but I would not say he is one to overly obsess over them. He does imagine play too. I guess my biggest concerns are the flapping and language gaps. Help! Should I take him to a specialist for a DX? If so, what type of dr?

His pediatrician recommended a Dr whose official specialty is Pediatric Developmental Behavioral Health. I just keep getting conflicting reports from the 2 OTs he works w/. They will not DX at his age in the school system. The one stricter OT is more worried about him than the other. I think part of it is he does not respond well to a strict personality, as he is more shy.