My two year old talking issues

My two year old can understand everything I say. When I tell him to do something he will do it. He can say many words. I can understand these words when he does. He just rarely talks. This is frustrating. He won’t repeat words when ask. If I ask him what something is he won’t say it. But I may hear the answer later on when he is just talking to him self. Out of no where he will say things . I read to him all the time. I can lay down three pictures and ask him to point out the cow. He does it no problem. He can even draw circle, squares, and etc. He can put puzzles together. His attention span is actually pretty good. Pediatrician thinks he doesn’t need speech therapy. Does anyone been thru this before? Any tips will help!