What Causes Behavioural Changes In A Child?

my family needs help. we have 3 children. 9, 6 and 16 months. the 9 year old boy has been a behavioral problem for years. he would often hit me when he was just 3-4 and often screams and yells when he doesn t get his way. and this is not a case of lazy parenting. we punish when punishment is needed and are consistent with all of that. we never know what will trigger his outbursts. tonight I asked him to take his toys off the counter, he refused so I put all of the toys that were on the counter into a bin and put them in my closet and told him he may have them back another day, and it turned into a 2 hour screaming fit from him. he just went to bed and it is midnight. the smallest thing can flip the switch and he will go from good boy to bad boy in the blink of an eye. we have just dealt with it all these years because doctors told us it was to get attention. well I disagree, we give him a lot of attention. another dr said parts of his brain work like a 3 year old and others like a 5 year old (he was 5 at that time) and eventually it will all catch up to the same place. well really our family cant take any more of his outburst. we need help. we just moved about a year and a half ago and I am having a hard time finding a place to get help. feels like docs here don t really know where to send us for help.