Should I take my son to the doctor?

My son is 3 years old and has always been a little bit behind other kids his age developmentally. In the last 6 months or so he will have an "episode" where he will say he wants to do something and when go to do it he screams and cries no. He will flap his arms and scream and cry "I want to," and "I don't want to," for up to 15 minutes. Is this a normal tantrum or could it be a form of autism? My doctor has told me he does not think he has autism, just that he is a little bit behind because he is a boy. He is very sociable with adults and kids, and he usually will do what you ask of him, it is just maybe once or twice a month he has a meltdown. Should I take him to a child psychologist? Any info will be helpful. Thanks