5 year old not adjusting to Kindergarten.

My son is currently is Kindergarten but is having behavioral issues and i can’t get him to have more good days. His father and I have been separated for almost four years. Some weeks he has good days but now since we do four days and three days spilts he’s been having issues. He is hitting and throwing things. I don’t believe that I should have to whoop him every time and nor do I feel I should yell at him. Have any of you mommies gone they this and how did you revert their behavior.