I have a child with similar issues. It may be as small as needing a change in medication or in my case a wrong diagnosis. We were told my dd had adhd and anxiety when she was in 1st grade. Now that she is in 4th grade her behavior is out of control. I did some research about childhood bipolar disorder. Usually misdiagnosed as adhd. He might need a mood stabilizer instead of or added to his current medications. Lamictal is what my dd is on currently. Talk to your prescribing doctor and tell them the change in behavior.
If it is an early onset of bipolar, stimulants make the child's anger and aggression excessive instead of better. That is why a mood stabilizer is given.