It's fine to get him investigated and the right place to start is a paed. You need to find a paed that specialises in this for the best help.

At 16 months no Doctor worth his degree will diagnose him with ASD - as you know the spectrum is very very broard. You are right that early intervention is important & it is. My DD14 has ASD (aspergers) and she clearly displayed issues from a very small baby. She wasn't formally diagnosed until she was 12.

Get an appointment and an appropriate specialist will likely shine a light on this.