What to do with my defiant child only in 1st Grade?

My son is 6 years old and in 1st Grade he has been going to this school for three years now. Last year was not as bad as this year. This year he is in the principals office nearly everyday no exaggerating on this. I have signed 8 reports in my son all either hitting, spitting, punching,stabing someone with a pencil, exposing himself during bathroom break others are exposing themselves to my son,fighting,talking back to the teachers,staff,and principals and to me as well at home. My son's behavior is totally out of control. At home is not nearly as bad as it is at school. The school told me on mre inncident will resolve in going to Alternative school. Well that was the last inncident and I don't want him to go, My son is a very loving and sweet boy. The pricipal is labeling my son as a bully because one day he took another child's iceream. I have eaten lunch with my son twice this year and alot of those kids are out of control. A fifth grader tried to get up just to get something to drink and was yelled at for asking? Idon't know if my son his rebeling towards someone or something . I am taking him to the doctor as soon as possible to get him to get him evaluated. At 9:30 the school tells me to come pick him up it is after 9:30 he won't be counted late. I know they are tired of dealing with my son but what about his education? I am thinking about homeschooling him myself. He can't control his behavior around a large group of children. I even tried to put him on a diet. he did well for a month and went back to being defiant. What should I do? I am worried for my son I love him so much. My son Listen to his father only. Me sometimes, but he demands me, talks back to me, Said he hates me then apoligizes. I am so worried. Parents, Anyone, any advice? My son acts like he could do what ever he wants untill dad gets home.