Hello and thank you for consulting JA,
I certainly agree with the above recommendations regarding a behavior management plan which is appropriate for voluntary behaviors. It is possible though that his behaviors are involuntary (the increase activity) if he suffers from Attention Deficit Hyperactivity Disorder (ADHD). ADHD is usually not diagnosed until an older age BUT in severe cases it is diagnosed earlier. Here are the diagnosis criteria: http://www.cdc.gov/ncbddd/adhd/diagnosis.html
You should contact the primary doctor about ways to get it diagnosed in your country. In the states is is the primary doctor, child psychologist or psychiatrist that diagnoses. Medication is the treatment. The behavior management is more about creating an environment where the child can function better (i.e., sit close to teacher for frequent reminders).
The eating is a separate issue. It is also a behavior in which a parent cannot "force" change. So the recommendation is to always place good nutrition in front of him for each meal and let him determine the quantity he will eat. Put small portions on the plate. Snack of fruit between meals if he wants. If he still choses to not eat even though he is very hungry, give him a multivitamin so that you know his vit and mineral needs are met. If he is losing weight it becomes more of a medical problem and the doctor may want him to have a suppliment (Pediasure).
One complicating fact that is relevant to both problems is that the ADHD meds suppress appetite.
Most parents are resistant to the idea of medication. It is when the behavior is interfering with his functioning (in school for instance) that you might want to consider a trial period (a few weeks) to see what happens.
I hope this is helpful....