DevPed muna or OT muna for suspected ASD

my son is 22 mos old, ndi nakakapagsalita, no eye contact and ndi palagi lumilingon pag tinawag name nya like out of 7 calls , 2 times lang sya lilingon Taz ignore after. he doesn't smile back pa pag nginitian mo. I booked for DevPed na pero UNG DevPed schedule next month pa pero UNG therapist available agad pero not sure if try ko muna UNG mga therapist assessment bago UNG DevPed Kasi tagal pa schedule Ng DevPed nya. Any input mga sis? TIA