Sorry you are having to deal with this. I always hate being the first one to respond to a new person's post just because there are so many questions to be asked to get a clear picture of the whole situation. Please bear with those of us that are responding first.
How old is your son? What kind of behaviors specifically is he displaying? Has he ever been evaluated by a psychiatrist, psychologist, or neuropsychologist? Does he have any diagnoses? Is he or has he ever been on any kind of medications? Are there any mental health issues on either side of the family tree (diagnosed or suspected and should be)? I assume it is just the two of you. Change can be hard for kids to handle expecially if they aren't capable of expressing it. Sometimes this comes out as anger and aggression. Do you work? What did he "get kicked out" of school for and for how long?
Welcome to our little corner of the world. You have come to a great place with a lot of personal experience from many who have been where you are (and worse). There is also a tremendous amount of support from some very strong shoulders. Others will be along, probably with more questions until we get a full understanding of the situation so we can steer you in the right direction.
In the meantime, many supportive {{{{(((HUGS)))}}}} to you.