ADHD, delayed speech. His condition?

My son is 2 yrs, born premature and low birth wt.(1840g). We suspect he has ADHD. Speech is delayed. Vomits solid feed. Doesn't say mama/papa. Extremely active. On the plus side- laughs and smiles a lot, is jovial, loves outdoor, and since last 4-6 months is emotionally getting attached to parents, started interacting and playing with twin sister, eats pureed solids when distracted, good motor skills. He may be having a mild condition but we want it diagnosed to be able to attend to his needs properly. At the moment we don't know how to get it diagnosed. We have gone through many ASD checklists. Responses to those checklists taken at 2 month intervals have been changing given that he has been outgrowing quite a few problematic symptoms. Kindly suggest how best to diagnose and attend to his condition. Can a pediatric neurologist ascertain his condition?