A referral to a psychologist might be moRe helpful than a paediatrician I suspect - you need advice and support about how to manage him (not necessarily counselling for him - but that may be an option too). A paed will consider things medically and probably won't spend the time on how to manage the behavioural stuff that you might need.

Triple P has good research behind it - but can be a bit heavy on the theory which can put some people off, or make it a bit difficult. Changes can be hard for kids - keep at it, you are trying and that's important.