Child Has Unclear Speech, Limited Speech. What To Do?

My son can complete a sentence in one or two words but it is not very clear. He speaks when somebody requests him to say. Even he does not ask for water in his own word ,he use to indicate his hand to the glass. When he is alone ,he sings and laughs himself. His all words are not unclear, sometimes we can easily understand his words or sentence. His reaction or response is normal,hearing is normal. He can easily catch any tune or song after watching television.He don't have any physical problem ,good health. He is 3.4 years old. What should I do ?
Thanks.