adhd child aggressive...help

I have a 7 year old child who becomes frustrated very easily and throws terrible tantrums.  Its very hard for me to deal with this since people look at me as if I have raised my child wrong.  The truth of the matter is that nobody in the outside can understand this unless they have lived with a adhd child.  I need help....... Yesterday he was suspended from school because another child told on him, and he told this child  " I am going to kill you.."  I know my child, and I know he does not have malice, I dont think he meant it the way it sounds.  I know my son did not say this with the intention of shooting another child.  The truth of the matter is that those are things that we cannot say and I dont think he understand the extent of what was said.  I am at a point where I dont know what else to do, I cry out of frustration because I dont know how else to make my son understand that he needs to control himself.  I know his teachers do not like him and it hurts me to know that my child is going through this with his teachers as well as with his classmates.  He was on adderall (adderrall) for a few months, but all these dr. visits and treatments are expensive, and he does not have insurance.  Until I can get back on my feet financially I am trying to deal with it on my own......someone help