My 3 year old toddler is very busy has trouble sitting still and has a limited vocabulary is this a problem?

Although she know her abc's / 123's / colors / cognitive skills/ comprehension skills. She is an only child and lacks social skills though she has been in daycare with other children. I wonder if she is just delayed or are these signs or of a bigger issue, autism, mental disorder, or attention deficit. (My concern is here inability to sit still for a period of time or to build sentences) Do you recognize any of these issues and can you tell me what might be the issue or where to go directly for help.