I have a VERY strong-willed 3-year old...

This little boy is extremely strong-willed. He has acted SO ugly today. He doesn't think he has to listen, will throw a huge fit if I tell him he can't do what he wants, and then he ignores me and does it anyway. If I put him in time out or take something from him, the rage flows on. I'm really hoping that we can find out what is going on with him over the next couple of weeks. We have a 2-hour home visit tomorrow with all of our behavioral therapists and then next Tuesday, we bring him in for all of his cognitive testing. Please, Lord, give me some answers and let's start getting him better. This little boy thinks that he runs this house and if we fight him on anything he's just going to do it anyway. That's his mindset anyway. Tracie and Emma are trying to get away with some of his behaviors now as well and I really want a put a stop to it all as much as we can. I just don't know what to do with him anymore...I've never met such a strong-willed toddler...I love him to pieces, but he just doesn't give up...