Could my child be PDD?

My child is 3.5 yrs old and has a speech delay (mainly articulation) and also has sensory processing issues as well-He is sensory seeking and a very picky eater (reflux as a baby).  He is very smart and loves to play with other children and is very responsive.  He does have trouble with transitions but is getting better with his OT.  He has a self soothing technique that he has been doing since he was 2 in which is stiffins his arms and balls his fist and leans over when is is excited or "proud" of an accomplishment or is overstimulated. He has changed this technique within the last month with now bringing his hands up to his face and shaking then slightly and making a grimice for about 2 seconds and then he goes back to what he is going. His OT says it could be an anticipatory response and to redirect it because it looks a bit awkward.  I have noticed he is doing it more frequently now when excited but he is also developing with postive progress.  Is this self soothing technique something we should worry about?  I don't feel it is a stim? Should we see a Developmental Peditrician and have him re-tested?  Is this a PDD trait? Thank you!