D..
He's not the only one having trouble with the transition to a new home and country, C.. You are too. You are missing Singapore and all that you were used to.
I hope that you realize that saying that you USED to be proud of him until you came to America is not a good thing to say or feel. I hope you didn't write the English well, and that you don't really mean that you are no longer proud of your son. You should always be proud of your son.
He is having a hard time. Do not let him hit or pinch you. Take his hands firmly in yours and don't let go - say to him "Hands are for helping, not hurting. You may NOT hurt with your hands." Then put him in his room for time out for a few minutes. When you let him out of his room, make him say that he is sorry. Be 100% consistent with this so he finally understands that he may not hit or pinch. It will take a long time to get him to understand.
You need to find some activities for him. Check with a YMCA in your area. Take him to park ANYWAY and just stand at the slide. Do not run even though he asks you to. He is not your boss. YOU are the boss. You are not his friend - you are his parent. He does not tell you what to do. He needs to run and play and keeping him in the house just because you cannot run is not helpful to him.
Very soon he will be ready to potty train. Then you can get him into preschool. That will help.
Good luck!
Dawn