my 1year 6month is not talking

What should I do to help my son learn to talk I took my son to the doctor for a check up like 2months ago and they said he should be saying atleast 3words but he wasn't nd now he's 1year 6months and only says "mum" and wants to say "ball" but still hasn't really gotin it yet. I'm really worried cuz his doctor said by next check up if he's not talking then we have to worry a little ,nd he's not talking but we think cuz me his mom I have always been a quit person and to myself and also his dad is just the same way to so.... Can that be the reason why my son doesn't talk? Or am I doing something wrong? What can I do to get my son talking I try what my family says on when he wants something I say the name to him then give it to him! And also I know my son does pick up stuff like I can tell him give me the ball were is your juice well stuff like that and he we bring me them............. SO PLZ SOME ONE RESPOND AND TELL ME WHAT SHOULD I DO? AND SHOULD I BE REALLY WORRIED?