Kindergarten sudden behavior change

I'm worried about my son. 5 weeks into a great start of kindergarten he became difficult to manage at school. I had already noticed changes in his behavior from certain food and decided I would involve myself further into restricting certain food from his diet. This worked successfully for the entire of second term. He was often getting good behavior awards and great reports from teachers. However, we are now in term 3 and despite having a fantastic first week he has had another sudden change in behavior. This time he has become aggressive and he has even been suspended as his behavior was becoming dangerous (he was leaving the classroom and even crawled under the school building)
I know I had a small slip up with his diet but I've made the mistake once before and he's 'recovered' within days. It has been over a week. The only changes in his life at the moment have been his uncle has come to stay with us and his "nanny" has moved away (both in the same week) This hasn't seemed to affect him at home. (Also I am 7 months pregnant.) I'm not 100% sure this is the trigger. What do I do?

[Kevin Kennedy, Ph.D.]

He's experiencing a lot of change in his social environment, and that is almost always a formula for unstable behavior in young children. Be sure to maintain a consistent, predictable routine - that is the most important thing. If there is any 'rule breaking' at school, be sure to follow up at home and be sure the school is setting firm limits as well.